Consolidated Statements of Changes in Shareholders' Equity (USD $) In Thousands, except Share data	Total	Common Shares [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Balance, Amount at Dec. 31, 2009	$ 240,269	$ 1,714	$ 177,246	$ 54,119	$ 7,190
Balance, Shares at Dec. 31, 2009		17,141,710
Net income	44,208			44,208
Unrealized loss on derivative instrument net of taxes	(90)				(90)
Translation adjustment	(1,710)				(1,710)
Tax benefit on exercise of stock options	2,222		2,222
Share-based compensation expense	8,138		8,138
Common shares issued	7,854	58	7,796
Common shares issued, Shares		584,935
Balance, Amount at Dec. 31, 2010	300,891	1,772	195,402	98,327	5,390
Balance, Shares at Dec. 31, 2010		17,726,645
Net income	(1,073)			(1,073)
Unrealized loss on derivative instrument net of taxes	(437)				(437)
Translation adjustment	(3,192)				(3,192)
Purchase of minority interest	(517)		(517)
Tax benefit on exercise of stock options	1,737		1,737
Reclassification for tax benefit on exercise of stock options	(8,999)		(8,999)
Share-based compensation expense	6,648		6,648
Common shares issued	20,113	74	20,039
Common shares issued, Shares		738,799
Balance, Amount at Dec. 31, 2011	315,171	1,846	214,310	97,254	1,761
Balance, Shares at Dec. 31, 2011	18,465,444	18,465,444
Net income	51,295			51,295
Unrealized loss on derivative instrument net of taxes	263				263
Translation adjustment	480				480
Share-based compensation expense	6,303		6,303
Common shares issued	25,586	88	25,498
Common shares issued, Shares		873,885
Balance, Amount at Dec. 31, 2012	$ 399,098	$ 1,934	$ 246,111	$ 148,549	$ 2,504
Balance, Shares at Dec. 31, 2012	19,339,329	19,339,329