Basis of Presentation - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Company And Summary Of Significant Accounting Policies [Line Items]
Losses related to loss contracts	$ 1,500,000	$ 1,600,000	$ 3,700,000	$ 2,000,000
Defense contract audit agency completed cost audits			Contract costs on U.S. government contracts are subject to audit and review by the Defense Contracting Management Agency (DCMA), the Defense Contract Audit Agency (DCAA), and other U.S. government agencies, as well as negotiations with U.S. government representatives. The Company’s incurred cost audits by the DCAA have not been concluded for fiscal years 2016 and 2017. As of September 30, 2017, the DCAA had completed its incurred cost audit for fiscal year 2004 and approved the Company’s incurred cost claims for fiscal years 2005 through 2015 without further audit. Although the Company has recorded contract revenues subsequent to fiscal year 2015 based upon an estimate of costs that the Company believes will be approved upon final audit or review, the Company does not know the outcome of any ongoing or future audits or reviews and adjustments, and if future adjustments exceed the Company’s estimates, its profitability would be adversely affected.
Advertising costs	2,300,000	800,000	$ 3,500,000	1,600,000
Capitalized interest expense	16,100,000	11,600,000	30,700,000	21,800,000
Total capitalized costs related to patents	3,200,000		3,200,000		$ 3,200,000
Total capitalized costs related to orbital slots and other licenses	15,400,000		15,400,000		15,400,000
Accumulated amortization of patents, orbital slots and other licenses	2,300,000		2,300,000		2,100,000
Debt issuance costs capitalized	9,800,000		9,800,000	6,100,000
Capitalized costs, net, related to software developed for resale	225,163,000		225,163,000		203,686,000
Capitalized cost related to software development for resale	20,000,000	19,700,000	37,800,000	40,700,000
Amortization expense of capitalized software development costs	6,600,000	8,700,000	16,300,000	16,400,000
Self-insurance liability	3,900,000		3,900,000		4,200,000
Repurchase and immediate retirement of treasury shares pursuant to vesting of certain RSU agreements			2,483,000
Stock-based compensation expense	16,000,000	12,600,000	31,490,000	25,418,000
Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedging [Member] | Foreign Currency Forward Contracts [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Notional value of foreign currency forward contracts outstanding	1,500,000		1,500,000		2,600,000
Gains or losses from ineffectiveness of derivative instruments	0	0	$ 0	0
Foreign currency forward contracts maturity, maximum			36 months
Accounting Standards Update 2016-01 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities (ASC 825-10). ASU 2016-01 requires that most equity investments (except those accounted for under the equity method for accounting or those that result in consolidation of the investee) be measured at fair value, with subsequent changes in fair value recognized in net income (loss). The new guidance also impacts financial liabilities under the fair value option and the presentation and disclosure requirements for financial instruments. The new guidance should be applied by means of a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption. ASU 2016-01 will become effective for the Company in fiscal year 2019, with early adoption permitted with certain stipulations. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2016-02 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In February 2016, the FASB issued ASU 2016-02, Leases (ASC 842). ASU 2016-02 requires lessees to recognize most leases on their balance sheets as lease liabilities with corresponding right-of-use assets and eliminates certain real estate-specific provisions. The new guidance will become effective for the Company beginning in the first quarter of fiscal year 2020, with early adoption permitted. ASU 2016-02 will be adopted on a modified retrospective transition basis for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2016-05 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In March 2016, the FASB issued ASU 2016-05, Derivatives and Hedging (ASC 815). ASU 2016-05 clarifies that a change in the counterparty to a derivative instrument, in and of itself, does not require dedesignation of a hedging relationship. This guidance became effective for the Company beginning in the first quarter of fiscal year 2018. The Company adopted this guidance in the first quarter of fiscal year 2018 on a prospective basis and the guidance did not have a material impact on the Company’s consolidated financial statements and disclosures.
Accounting Standards Update 2016-06 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In March 2016, the FASB issued ASU 2016-06, Derivatives and Hedging (ASC 815). ASU 2016-06 clarifies the requirements for assessing whether contingent put or call option in a debt instrument qualifies as a separate derivative. The new guidance is required to be applied on a modified retrospective basis to all existing and future debt instruments of the fiscal year for which the amendments are effective. This guidance became effective for the Company beginning in the first quarter of fiscal year 2018. The Company adopted this guidance in the first quarter of fiscal year 2018 on a modified retrospective basis and the guidance did not have a material impact on the Company’s consolidated financial statements and disclosures.
Accounting Standards Update 2016-13 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In June 2016, the FASB issued ASU 2016-13, Financial Instruments — Credit Losses (ASC 326). ASU 2016-13 requires credit losses on most financial assets measured at amortized cost and certain other instruments to be measured using an expected credit loss model (referred to as the current expected credit loss (CECL) model). It also modifies the impairment model for available-for-sale debt securities and provides for a simplified accounting model for purchased financial assets with credit deterioration since their origination. The new guidance will become effective for the Company beginning in fiscal year 2021, with early adoption permitted. The new guidance is required to be applied on a modified-retrospective basis. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2016-15 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (ASC 230). ASU 2016-15 makes eight targeted changes to how companies present and classify certain cash receipts and cash payments in the statement of cash flows. The new standard will become effective for the Company beginning in fiscal year 2019, with early adoption permitted. The new standard will require adoption on a retrospective basis unless it is impracticable to apply, in which case the Company would be required to apply the amendments prospectively as of the earliest date practicable. The Company early adopted the guidance on a retrospective basis in the second quarter of fiscal year 2018 and as a result cash payments for debt prepayment and extinguishment are classified as cash outflows for financing activities. Otherwise the adoption of this guidance did not have a material impact on the Company’s consolidated financial statements and disclosures.
Accounting Standards Update 2016-16 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In October 2016, the FASB issued ASU 2016-16, Income Taxes (ASC 740). ASU 2016-16 requires that an entity should recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs as opposed to when the asset has been sold to an outside party. The new standard will become effective for the Company beginning in fiscal year 2019, with early adoption permitted. The new standard will require adoption on a modified retrospective basis through cumulative-effect adjustment directly to retained earnings as of the beginning of the period. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2016-17 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In October 2016, the FASB issued ASU 2016-17, Consolidation: Interests Held through Related Parties That Are Under Common Control (ASC 810). The amendments change how a reporting entity that is the single decision maker of a variable interest entity should treat indirect interests in the entity held through related parties that are under common control with the reporting entity when determining whether it is the primary beneficiary of that variable interest entity. The new standard became effective for the Company beginning in the first quarter of fiscal year 2018. The Company adopted this guidance in the first quarter of fiscal year 2018 on a retrospective basis and the guidance did not have a material impact on the Company’s consolidated financial statements and disclosures.
Accounting Standards Update 2017-01 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In January 2017, the FASB issued ASU 2017-01, Business Combinations: Clarifying the Definition of a Business (ASC 805). ASU 2017-01 clarifies the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The definition of a business affects many areas of accounting including acquisitions, disposals, goodwill, and consolidation. The new standard will become effective for the Company beginning in fiscal year 2019, with early adoption permitted with limitations. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2017-05 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In February 2017, the FASB issued ASU 2017-05, Other Income — Gains and Losses from the Derecognition of Nonfinancial Assets (ASC 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets. ASU 2017-05 clarifies the scope and accounting of a financial asset that meets the definition of an “in-substance nonfinancial asset” and defines the term “in-substance nonfinancial asset.” ASU 2017-05 also adds guidance for partial sales of nonfinancial assets. The standard will become effective for the Company in fiscal year 2019, with early adoption permitted. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2017-08 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In March 2017, the FASB issued ASU 2017-08, Receivables — Nonrefundable Fees and Other Costs (ASC 310-20): Premium Amortization on Purchased Callable Debt Securities. ASU 2017-08 amends the amortization period for certain callable debt securities held at a premium. The amendments require the premium to be amortized to the earliest call date. The standard will become effective for the Company beginning in fiscal year 2020, with early adoption permitted. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2017-09 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In May 2017, the FASB issued ASU 2017-09, Compensation — Stock Compensation (ASC 718): Scope of Modification Accounting. ASU 2017-09 provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. The standard will become effective for the Company beginning in fiscal year 2019, with early adoption permitted. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2014-09 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers. ASU 2014-09 requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to a customer. This guidance will replace most existing revenue recognition guidance and will be effective for the Company beginning in fiscal year 2019, including interim periods within that reporting period, based on the FASB decision in July 2015 (ASU 2015-14, Revenue from Contracts with Customers – Deferral of the Effective Date) to delay the effective date of the new revenue recognition standard by one year, but providing entities a choice to adopt the standard as of the original effective date. In March 2016, the FASB issued ASU 2016-08, Principal versus Agent Considerations (Reporting Revenue Gross versus Net), which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10, Identifying Performance Obligations and Licensing, which clarifies the implementation guidance on identifying performance obligations and the licensing implementation guidance. In May 2016, the FASB issued ASU 2016-12, Narrow-Scope Improvements and Practical Expedients, which provides practical expedient for contract modifications and clarification on assessing the collectability criterion, presentation of sales taxes, measurement date for non-cash consideration and completed contracts at transition. In December 2016, the FASB issued ASU 2016-20, Technical Corrections and Improvements to ASC 606, Revenue from Contracts with Customers, which provides for correction or improvement to the guidance previously issued in ASU 2014-09. These standards permit the use of either the retrospective or cumulative effect transition method. The Company currently plans to adopt the standard in fiscal year 2019 using the “modified retrospective method.” Under that method, the Company will apply the rules to all contracts existing as of April 1, 2018, recognizing in beginning retained earnings an adjustment for the cumulative effect of the change and providing additional disclosures comparing results to previous accounting standards. Upon initial evaluation, the Company believes the key changes in the standard that impact its revenue recognition relate to the deferral of commissions in the Company’s satellite service segment, which are currently expensed as incurred under the current standard. The requirement to defer incremental contract acquisition costs and recognize them with the transfer of the related good or service will result in the recognition of a deferred charge on the Company’s consolidated balance sheet and corresponding impact to the Company’s consolidated statement of operations and comprehensive income (loss).
Accounting Standards Update 2016-07 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In March 2016, the FASB issued ASU 2016-07, Investment — Equity Method and Joint Ventures (ASC 323). ASU 2016-07 eliminates the requirement to apply the equity method of accounting retrospectively when a reporting entity obtains significant influence over a previously held investment. This guidance became effective for the Company beginning in the first quarter of fiscal year 2018. The Company adopted this guidance in the first quarter of fiscal year 2018 on a prospective basis and the guidance did not have a material impact on the Company’s consolidated financial statements and disclosures.
Accounting Standards Update 2016-09 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In March 2016, the FASB issued ASU 2016-09, Compensation — Stock Compensation (ASC 718). ASU 2016-09 simplifies various aspects related to how share-based payments are accounted for and presented in the financial statements. The new guidance became effective for the Company beginning in fiscal year 2018. The Company adopted this guidance in the first quarter of fiscal year 2018. On a prospective basis the Company recognizes excess tax benefits or deficiencies on vesting or settlement of awards as discrete items within income tax benefit or provision within net income (loss) and the related cash flows classified within operating activities. With respect to the forfeiture accounting policy election, the Company elected to account for forfeitures as they occur, adopted on a modified retrospective basis as a cumulative effect adjustment to retained earnings. The election to account for forfeitures as they occur did not have a material impact on the Company’s consolidated financial statements and disclosures.
Accounting Standards Update 2017-04 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In January 2017, the FASB issued ASU 2017-04, Intangibles — Goodwill and Other: Simplifying the Test for Goodwill Impairment (ASC 350). ASU 2017-04 removes Step 2 from the goodwill impairment test. The standard will become effective for the Company beginning in fiscal year 2021, with early adoption permitted. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2017-10 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In May 2017, the FASB issued ASU 2017-10, Service Concession Arrangements (ASC 853): Determining the Customer of the Operation Services. ASU 2017-10 provides clarity on determining the customer in a service concession arrangement. The standard will become effective for the Company beginning in fiscal year 2019, with early adoption permitted. The new standard will require adoption on a modified retrospective approach by recording a cumulative-effect adjustment to equity, beginning with the earliest period presented, or a retrospective approach. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Accounting Standards Update 2017-12 [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Description of new accounting pronouncements			In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. ASU 2017-12 improves the financial reporting of hedging relationships to better portray the economic results of an entity’s risk management activities in its financial statements and make certain targeted improvements to simplify the application of the hedge accounting guidance in current GAAP. The amendments in this update better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and presentation of hedge results. The standard will become effective for the Company beginning in fiscal year 2020, with early adoption permitted. The Company is currently evaluating the impact of this standard on its consolidated financial statements and disclosures.
Employee Stock Options [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Incremental tax benefit from stock options exercised and restricted stock unit awards released		0		0
Restricted Stock Units [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Incremental tax benefit from stock options exercised and restricted stock unit awards released		$ 0		$ 0
Minimum [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)			2 years
Estimated useful life, years			2 years
Maximum [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)			24 years
Estimated useful life, years			10 years
Maximum [Member] | Software Development Costs [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Estimated useful life, years			5 years
Property and Equipment, Net [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property and equipment	1,287,903,000		$ 1,287,903,000		1,202,589,000
Accumulated depreciation and amortization	710,386,000		$ 710,386,000		661,981,000
CPE Leased Equipment [Member] | Minimum [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)			4 years
CPE Leased Equipment [Member] | Maximum [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property, equipment and satellites, estimated useful life (years)			5 years
CPE Leased Equipment [Member] | Property and Equipment, Net [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Property and equipment	260,219,000		$ 260,219,000		271,917,000
Accumulated depreciation and amortization	$ 162,400,000		$ 162,400,000		$ 158,200,000
Common Stock Held in Treasury [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Shares of common stock held in treasury	0		0		0
Purchase of treasury shares pursuant to vesting of certain RSU agreements, shares			36,666	34,204
Repurchase and immediate retirement of treasury shares pursuant to vesting of certain RSU agreements			$ 2,500,000	$ 2,500,000
Common Stock [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Common stock issued based on the vesting terms of certain restricted stock unit agreements			106,741	102,103
Unfavorable Regulatory Action [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Accrued reserves	$ 1,300,000		$ 1,300,000		$ 1,800,000
Indemnification Agreement [Member]
Company And Summary Of Significant Accounting Policies [Line Items]
Accrued reserves	$ 0		$ 0		$ 0