Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 48,879	$ 42,282	$ 22,429
Other comprehensive income, net of tax:
Foreign currency translation adjustments	4,272	(2,866)	868
Unrealized holding gains (losses) on short-term investments arising during period	2	(3)	(6)
Defined benefit pension plan:
Net loss arising from period (net of tax effect of $(62),$(629), and $(66)	(119)	(972)	(28)
Amortization of net acturial loss included in net periodic pension cost (net of tax effect of $97, $48, and $32)	152	75	50
Net change in defined benefit pension plan	33	(897)	22
Cash flow hedges:
Unrealized losses on change in fair value of interest rate swap contracts (net of tax effect of $(26), $(387), and $0)	(282)	(684)
Reclassification adjustment for losses included in net income (net of tax effect of $151, $41, and $0)	242	66
Net change in cash flow hedges	(40)	(618)
Other comprehensive income, net of tax	4,267	(4,384)	884
Total comprehensive income, net of tax	$ 53,146	$ 37,898	$ 23,313