Stockholders' Equity - Stock Options Activities (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding at the beginning of the year (in shares)	1,456,285
Granted (in shares)	0
Exercised (in shares)	(744,636)
Forfeited (in shares)	(1,981)
Options outstanding at the end of the period (in shares)	709,668	1,456,285
Options exercisable at the end of the year (in shares)	687,508
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Options outstanding at the beginning of the year, weighted average exercise price (in dollars per share)	$ 16.172
Granted, weighted average exercise price (in dollars per share)	0.000
Exercised, weighted average exercise price (in dollars per share)	14.469
Forfeited, weighted average exercise price (in dollars per share)	32.473
Options outstanding at the end of the period, weighted average exercise price (in dollars per share)	17.941	$ 16.172
Options exercisable at the end of the year, weighted average exercise price (in dollars per share)	$ 17.856
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options outstanding at the beginning of the year, aggregate intrinsic value	$ 24,810	$ 47,152
Options exercisable at the end of the year, aggregate intrinsic value	$ 24,093
Options outstanding at the beginning of the year, weighted average remaining contractual life (Year)	4 years 6 months 5 days	4 years 10 months 27 days
Options exercisable at the end of the year, weighted average remaining contractual life (Year)	4 years 5 months 8 days