Consolidated Statements Stockholders' Equity (USD $)	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance, Value at Dec. 31, 2009	$ 170,743,000	$ 3,443,000	$ (76,000)	$ 158,404,000	$ 8,623,000	$ 349,000
Beginning Balance, Issued Shares at Dec. 31, 2009		34,474,608
Beginning Balance, Treasury Shares at Dec. 31, 2009			(40,509)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	59,019,000				59,019,000
Cumulative translation adjustment	6,530,000					6,530,000
Exercise of stock options, Shares		1,252,785
Exercise of stock options, Value	1,236,000	125,000		1,111,000
Stock Repurchased and Retired During Period, Shares		(669,978)
Stock Repurchased and Retired During Period, Value	(10,650,000)	(67,000)		(10,583,000)
Stock Issued During Period, Shares, Conversion of Convertible Securities		760,040
Stock Issued During Period, Value, Conversion of Convertible Securities	1,712,000	76,000		1,636,000
Deferred compensation and amortization related to options and restricted stock	1,850,000			1,850,000
Share subscribed for business acquisition, Value	828,000			828,000
Vesting of restricted stock, Shares		240,336
Vesting of restricted stock, Value	0	25,000		(25,000)
Forfeiture of certain shares to satisfy exercise costs and the recipients income tax obligations related to stock options exercised and restricted stock vested	0
Dividends paid	0
Ending Balance, Value at Dec. 31, 2010	231,268,000	3,602,000	(76,000)	153,221,000	67,642,000	6,879,000
Ending Balance, Issued Shares at Dec. 31, 2010		36,057,791
Ending Balance, Treasury Shares at Dec. 31, 2010			(40,509)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	71,378,000				71,378,000
Cumulative translation adjustment	(11,403,000)					(11,403,000)
Exercise of stock options, Shares		69,509
Exercise of stock options, Value	51,000	8,000		43,000
Stock Repurchased and Retired During Period, Shares		(3,510,973)
Stock Repurchased and Retired During Period, Value	(63,659,000)	(351,000)		(63,308,000)
Stock Issued During Period, Value, Conversion of Convertible Securities	(1,851,000)			(1,851,000)
Deferred compensation and amortization related to options and restricted stock	2,205,000			2,205,000
Share subscribed for business acquisition, Shares		3,650,914
Share subscribed for business acquisition, Value	87,476,000	365,000		87,111,000
APIC adjustment for stock options	2,111,000			2,111,000
Vesting of restricted stock, Shares		151,144
Vesting of restricted stock, Value	0	14,000		(14,000)
Forfeiture of certain shares to satisfy exercise costs and the recipients income tax obligations related to stock options exercised and restricted stock vested	0
Dividends paid	(1,461,000)				(1,461,000)
Ending Balance, Value at Dec. 31, 2011	316,115,000	3,638,000	(76,000)	179,518,000	137,559,000	(4,524,000)
Ending Balance, Issued Shares at Dec. 31, 2011	36,418,385	36,418,385
Ending Balance, Treasury Shares at Dec. 31, 2011			(40,509)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	70,569,000				70,569,000
Cumulative translation adjustment	(2,394,000)					(2,394,000)
Exercise of stock options, Shares		1,361,542
Exercise of stock options, Value	1,020,000	137,000		883,000
Stock Repurchased and Retired During Period, Shares		(983,818)
Stock Repurchased and Retired During Period, Value	(18,374,000)	(99,000)		(18,275,000)
Deferred compensation and amortization related to options and restricted stock	2,083,000			2,083,000
Share subscribed for business acquisition, Shares		296,560
Share subscribed for business acquisition, Value	0	30,000		(30,000)
APIC adjustment for stock options	1,162,000			1,162,000
Vesting of restricted stock, Shares		89,308
Vesting of restricted stock, Value	0	8,000		(8,000)
Forfeiture of certain shares to satisfy exercise costs and the recipients income tax obligations related to stock options exercised and restricted stock vested, Shares		(50,200)
Forfeiture of certain shares to satisfy exercise costs and the recipients income tax obligations related to stock options exercised and restricted stock vested	(992,000)	(5,000)		(987,000)
Dividends paid	(7,034,000)				(7,034,000)
Ending Balance, Value at Dec. 31, 2012	$ 362,155,000	$ 3,709,000	$ (76,000)	$ 164,346,000	$ 201,094,000	$ (6,918,000)
Ending Balance, Issued Shares at Dec. 31, 2012	37,131,777	37,131,777
Ending Balance, Treasury Shares at Dec. 31, 2012			(40,509)