CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - UNAUDITED (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 5,233	$ 15,300	$ 24,327	$ 42,270
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	(10,260)	6,359	(6,185)	(3,330)
Unrealized holding gains (losses) on short-term investments arising during period	(17)	81	(7)	25
Defined benefit pension plan:
Net loss arising from period (net of tax effect of $0, $0, $0, and $(119))				(183)
Amortization of net actuarial loss included in net periodic pension cost (net of tax effect of $0, $0, $0, and $28)				43
Partial settlement of pension plan liability (net of tax effect of $0, $0, $0 and $336)				546
Net change in defined benefit pension plan				406
Cash flow hedges:
Unrealized gains on change in fair value of interest rate swap contracts (net of tax effect of $0, $199, $110, and $549)		313	195	865
Reclassification adjustment for losses included in net income (net of tax effect of $0, $(101), $(55), and $(280))		(160)	(97)	(442)
Net change in cash flow hedges		153	98	423
Other comprehensive income (loss), net of tax	(10,277)	6,593	(6,094)	(2,476)
Total comprehensive income (loss), net of tax	$ (5,044)	$ 21,893	$ 18,233	$ 39,794