Stock-Based Compensation - Equity Awards Outstanding and Exercisable (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Stock options
Number of Stock Options
Options, outstanding at beginning of period (in shares)	851,573
Options, granted (in shares)	0	0
Options, exercised (in shares)	(148,255)
Options, forfeited (in shares)	(1,000)
Options, outstanding at end of period (in shares)	702,318	851,573
Options, exercisable (in shares)	697,818
Weighted-Average Exercise Price
Options, weighted average exercise price, beginning of period (in usd per share)	$ 13.21
Options, weighted average exercise price, granted (in usd per share)	0.00
Options, weighted average exercise price, exercised (in usd per share)	15.52
Options, weighted average exercise price, forfeited (in usd per share)	23.31
Options, weighted average exercise price, end of period (in usd per share)	12.70	$ 13.21
Options, weighted average exercise price, exercisable (in usd per share)	$ 12.63
Weighted-Average Remaining Term
Options, outstanding, weighted average remaining term	3 years 19 days	4 years 5 months 8 days
Options, exercisable, weighted average remaining term	3 years 11 days
Restricted stock units
Shares
Outstanding at beginning of period (in shares)	1,041,554
Granted (in shares)	532,537
Vested (in shares)	(305,542)
Forfeited and canceled (in shares)	(182,921)
Outstanding at end of period (in shares)	1,085,628	1,041,554
Weighted-Average Grant Date Fair Value
Outstanding at beginning of period (in usd per share)	$ 41.96
Granted (in usd per share)	97.85
Vested (in usd per share)	39.01
Forfeited and canceled (in usd per share)	53.62
Outstanding at end of period (in usd per share)	$ 68.24	$ 41.96
Performance-based restricted stock units
Shares
Outstanding at beginning of period (in shares)	1,838,227
Granted (in shares)	470,251
Vested (in shares)	(1,085,748)
Forfeited and canceled (in shares)	(185,805)
Outstanding at end of period (in shares)	1,036,925	1,838,227
Weighted-Average Grant Date Fair Value
Outstanding at beginning of period (in usd per share)	$ 24.37
Granted (in usd per share)	58.49
Vested (in usd per share)	18.86
Forfeited and canceled (in usd per share)	36.10
Outstanding at end of period (in usd per share)	$ 43.51	$ 24.37
Cash-settled performance-based restricted stock units
Shares
Outstanding at beginning of period (in shares)	1,693,394
Granted (in shares)	15,385
Vested (in shares)	(564,465)
Forfeited and canceled (in shares)	(391,038)
Outstanding at end of period (in shares)	753,276	1,693,394

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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- 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).