Activity Under Stock Option Plans (Details) - Jun. 30, 2015 - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	Total
Number of Shares Underlying Stock Options
Outstanding as of December 31, 2014	668
Granted	0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 0
Exercised	(112)
Cancelled or expired	0
Outstanding as of June 30, 2015	556
Vested and expected to vest at June 30, 2015	556
Exercisable at June 30, 2015	556
Weighted Average Exercise Price per Share
Outstanding as of December 31, 2014	$ 15.57
Exercised	16.05
Cancelled or expired	0.00
Outstanding as of June 30, 2015	15.47
Vested and expected to vest at June 30, 2014 (usd per share)	15.47
Exercisable at June 30, 2014 (usd per share)	$ 15.47
Weighted Average Remaining Contractual Term
SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	2 years 6 months 4 days
Vested and expected to vest at June 30, 2015	2 years 6 months 4 days
Exercisable at June 30, 2015	2 years 6 months 4 days
Aggregate Intrinsic Value
Outstanding as of June 30, 2015	$ 26,247
Vested and expected to vest at June 30, 2015	26,247
Exercisable at June 30, 2015	$ 26,247