Accounting Pronouncements (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Mar. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets	$ 75,075	$ 79,393
Total assets	7,686,881	5,537,883
Long-term debt	2,900,524	2,453,405
Total liabilities and stockholder's equity	7,686,881	5,537,883
Adoption of ASU 2016-09, cumulative adjustment	49,572
Scenario, Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets		109,025
Total assets		5,567,515
Long-term debt		2,483,037
Total liabilities and stockholder's equity		5,567,515
Scenario, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets		(29,632)
Total assets		(29,632)
Long-term debt		(29,632)
Total liabilities and stockholder's equity		(29,632)
Scenario, Actual
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets		79,393
Total assets		5,537,883
Long-term debt		2,453,405
Total liabilities and stockholder's equity		$ 5,537,883
Accounting Standards Update 2016-09, Forfeiture Rate Component, Share-based Payment Award Component | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income tax assets, net	2,300
Accounting Standards Update 2016-09, Excess Tax Benefit Component | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred income tax assets, net	47,200
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of ASU 2016-09, cumulative adjustment	47,605
Retained Earnings | Accounting Standards Update 2016-09, Forfeiture Rate Component | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of ASU 2016-09, cumulative adjustment	2,000
Retained Earnings | Accounting Standards Update 2016-09, Forfeiture Rate Component, Share-based Payment Award Component | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of ASU 2016-09, cumulative adjustment	2,300
Retained Earnings | Accounting Standards Update 2016-09, Excess Tax Benefit Component | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of ASU 2016-09, cumulative adjustment	47,200
Additional Paid-in Capital | Accounting Standards Update 2016-09, Forfeiture Rate Component | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of ASU 2016-09, cumulative adjustment	$ (2,000)