Stock-Based Compensation (Restricted Stock) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018
Unvested restricted stock units and awards
Number of Shares
Balance at the beginning of the period (in shares)	2,161,347	1,766,639	1,766,639
Granted (in shares)		925,641
Vested (in shares)	(253,279)	(503,668)
Forfeited (in shares)	(27,324)	(27,265)
Balance at the end of the period (in shares)	1,880,744	2,161,347	1,880,744
Weighted-Average Grant Date Fair Value per Share
Balance at the beginning of the period (in dollars per share)	$ 41.59	$ 32.48	$ 32.48
Granted (in dollars per share)		55.21
Vested (in dollars per share)	31.13	34.05
Forfeited (in dollars per share)	39.78	30.79
Balance at the end of the period (in dollars per share)	$ 43.36	$ 41.59	$ 43.36
Additional disclosures
Unrecognized compensation expense related to shares	$ 73,482		$ 73,482
Unrecognized compensation expense weighted-average recognition period			2 years 2 months 12 days
Stock options
Additional disclosures
Unrecognized compensation expense weighted-average recognition period			1 year 4 months 24 days
Performance-based restricted stock unit awards
Number of Shares
Vested (in shares)		(26,000)

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made 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).

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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).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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