Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Outstanding at beginning of period (in shares)	23,231	37,495	79,408
Exercised (in shares)	(9,842)	(12,662)	(37,713)
Forfeited or expired (in shares)	(831)	(1,602)	(4,200)
Outstanding at end of period (in shares)	12,558	23,231	37,495
Vested and expected to vest at end of period (in shares)	12,558
Exercisable at end of period (in shares)	12,558
Weighted-Average Exercise Price
Outstanding at beginning of period (in usd per share)	$ 14.21	$ 13.77	$ 14.19
Exercised (in usd per share)	13.45	12.97	14.31
Forfeited or expired (in usd per share)	14.77	13.76	16.80
Outstanding at end of period (in usd per share)	14.77	$ 14.21	$ 13.77
Vested and expected to vest at end of period (in usd per share)	14.77
Exercisable at end of period (in usd per share)	$ 14.77
Weighted-Average Remaining Contractual Term, Outstanding	1 year 4 months 20 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	1 year 4 months 20 days
Weighted-Average Remaining Contractual Term, Exercisable	1 year 4 months 20 days
Aggregate Intrinsic Value, Outstanding	$ 188
Aggregate Intrinsic Value, Vested and expected to vest	188
Aggregate Intrinsic Value, Exercisable	$ 188