Share-Based Transactions - Nonemployee Share-Based Transactions, Cost and Tax Benefit (Details) - Nonemployee Shares [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Goods And Nonemployee Services Transaction [Line Items]
Total quarterly non-employee RSUs granted	124,471	155,996	235,735
Weighted-average measurement-date fair value per share, granted	$ 102.43	$ 75.69	$ 48.45
Illiquidity discounts		10.00%
Total equity awards expense recognized	$ 3,288	$ 980	$ 910
Quarterly incentive awards expense	9,484	10,821	10,517
Tax benefit associated with incentive awards	$ 2,437	$ 2,259	$ 3,674
Minimum [Member]
Share Based Goods And Nonemployee Services Transaction [Line Items]
Weighted-average measurement-date fair value per share, granted	$ 96.60	$ 67.82	$ 39.87
Illiquidity discounts			10.00%
Maximum [Member]
Share Based Goods And Nonemployee Services Transaction [Line Items]
Weighted-average measurement-date fair value per share, granted	$ 120.55	$ 91.88	$ 61.50
Illiquidity discounts			11.00%

Illiquidity discount on share based compensation awards fair value assumption.

No definition available.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

+ Details

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- Definition

The amount by which an asset or assets increased resulting from the transaction in which equity securities were issued to pay for goods or nonemployee services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.I)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 50
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68057994&loc=d3e25284-112666

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The number of shares or units of entity securities issued in the transaction in which equity securities were issued to pay for goods or nonemployee services.

+ References

+ Details

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- Definition

The amount of income tax expense reduction and deferred tax asset recorded in the transaction in which equity securities were issued to pay for goods or nonemployee services.

+ References

+ Details

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