Stockholders' Equity - Activity Under Stock Option Plans (Details) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
Number of Shares Underlying Stock Options
Outstanding as of December 31, 2016 | shares	222
Exercised | shares	(101)
Cancelled or expired | shares	(4)
Outstanding as of June 30, 2017 | shares	117
Vested and expected to vest at June 30, 2017 | shares	117
Exercisable at June 30, 2017 | shares	117
Weighted Average Exercise Price per Share
Outstanding as of December 31, 2016 | $ / shares	$ 14.90
Exercised | $ / shares	16.53
Cancelled or expired | $ / shares	18.16
Outstanding as of June 30, 2017 | $ / shares	13.39
Vested and expected to vest at June 30, 2017 | $ / shares	13.39
Exercisable at June 30, 2017 | $ / shares	$ 13.39
Weighted Average Remaining Contractual Term
Outstanding as of June 30, 2017	1 year 2 months 1 day
Vested and expected to vest at June 30, 2017	1 year 2 months 1 day
Exercisable at June 30, 2017	1 year 2 months 1 day
Aggregate Intrinsic Value
Outstanding as of June 30, 2017 | $	$ 16,049
Vested and expected to vest at June 30, 2017 | $	16,049
Exercisable at June 30, 2017 | $	$ 16,049