Activity Under Stock Option Plans (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Number of Shares Underlying Stock Options
Outstanding as of December 31, 2016 | shares	222
Granted | shares	0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price | $ / shares	$ 0
Exercised | shares	(82)
Cancelled or expired | shares	(4)
Outstanding as of March 31, 2017 | shares	136
Vested and expected to vest at March 31, 2017 | shares	136
Exercisable at March 31, 2017 | shares	136
Weighted Average Exercise Price per Share
Outstanding as of December 31, 2016 | $ / shares	$ 14.90
Exercised | $ / shares	17.35
Cancelled or expired | $ / shares	18.16
Outstanding as of March 31, 2017 | $ / shares	13.33
Vested and expected to vest at March 31, 2017 | $ / shares	13.33
Exercisable at March 31, 2017 | $ / shares	$ 13.33
Weighted Average Remaining Contractual Term
Outstanding as of March 31, 2017	1 year 4 months 6 days
Vested and expected to vest at March 31, 2017	1 year 4 months 6 days
Exercisable at March 31, 2017	1 year 4 months 6 days
Aggregate Intrinsic Value
Outstanding as of March 31, 2017 | $	$ 13,809
Vested and expected to vest at March 31, 2017 | $	13,809
Exercisable at March 31, 2017 | $	$ 13,809