Consolidated Statements of Stockholders Equity (USD $)	Total	Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2009	$ 474,049,000	$ 330,654,000	$ 66,000	$ 94,996,000	$ 235,726,000	$ (175,220,000)	$ (12,173,000)
Net income	107,896,000				107,896,000
Fair value of interest rate swaps, net of tax of $2,425	3,957,000						3,957,000
Other comprehensive income from currency exchange, net of tax	115,000						115,000
Total comprehensive income	111,968,000
Payment of dividends on convertible preferred stock	(7,635,000)	(7,635,000)
Conversion of convertible preferred stock to common stock in connection with initial public offering		(323,019,000)	45,000	279,433,000	43,541,000
Issuance of common stock	47,563,000		1,000	47,562,000
Balance at Dec. 31, 2010	625,945,000		112,000	421,991,000	387,163,000	(175,220,000)	(8,101,000)
Net income	147,335,000				147,335,000
Other comprehensive income from currency exchange, net of tax	(5,615,000)						(5,615,000)
Total comprehensive income	141,720,000
Repurchase of common stock	(443,000)					(443,000)
Issuance of common stock	44,214,000		2,000	44,212,000
Balance at Dec. 31, 2011	811,436,000		114,000	466,203,000	534,498,000	(175,663,000)	(13,716,000)
Net income	216,199,000				216,199,000
Other comprehensive income from currency exchange, net of tax	10,370,000						10,370,000
Total comprehensive income	226,569,000
Repurchase of common stock	(200,000,000)					(200,000,000)
Issuance of common stock	75,817,000		2,000	75,815,000
Balance at Dec. 31, 2012	$ 913,822,000		$ 116,000	$ 542,018,000	$ 750,697,000	$ (375,663,000)	$ (3,346,000)