Consolidated Statements of Changes in Stockholders' Equity (USD $) In Thousands, except Share data	Common Class A [Member]	Common Class B [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2009	$ 280,880	$ 468	$ 10,501	$ (3,850)	$ 19,039	$ 307,038
Balance (in Shares) at Dec. 31, 2009	22,036,000	3,762,000
Net income					13,719	13,719
Fair value of interest rate swap agreements, net of tax expense (benefit)				(1,019)		(1,019)
Issuance of stock in connection with employee stock plans	4,192					4,192
Issuance of stock in connection with employee stock plans (in Shares)	658,000
Shares forfeited by employees (in Shares)	(9,000)
Repurchase of Class A common stock	(1,626)					(1,626)
Repurchase of Class A common stock (in Shares)	(162,000)
Compensation for stock and stock option issuances and excess tax benefits from option exercises	1,361		471			1,832
Dividends paid					(3,919)	(3,919)
Balance at Dec. 31, 2010	284,807	468	10,972	(4,869)	28,839	320,217
Balance (in Shares) at Dec. 31, 2010	22,523,000	3,762,000
Net income					58,860	58,860
Fair value of interest rate swap agreements, net of tax expense (benefit)				361		361
Issuance of stock in connection with employee stock plans	5,654					5,654
Issuance of stock in connection with employee stock plans (in Shares)	438,000
Issuance of restricted stock to employees (in Shares)	11,000
Shares forfeited by employees (in Shares)	(5,000)
Repurchase of Class A common stock	(13,568)					(13,568)
Repurchase of Class A common stock (in Shares)	(772,000)
Compensation for stock and stock option issuances and excess tax benefits from option exercises	2,473		(54)			2,419
Dividends paid					(6,822)	(6,822)
Balance at Dec. 31, 2011	279,366	468	10,918	(4,508)	80,877	367,121
Balance (in Shares) at Dec. 31, 2011	22,195,000	3,762,000
Net income					80,362	80,362
Fair value of interest rate swap agreements, net of tax expense (benefit)				1,893		1,893
Issuance of stock in connection with employee stock plans	8,652					8,652
Issuance of stock in connection with employee stock plans (in Shares)	647,000
Issuance of restricted stock to employees (in Shares)	3,000
Repurchase of Class A common stock	(23,279)					(23,279)
Repurchase of Class A common stock (in Shares)	(929,000)
Class B commons stock converted to Class A common stock	125	(125)
Class B commons stock converted to Class A common stock (in Shares)	1,000,000	(1,000,000)
Compensation for stock and stock option issuances and excess tax benefits from option exercises	3,937		1,481			5,418
Dividends paid					(12,066)	(12,066)
Balance at Dec. 31, 2012	$ 268,801	$ 343	$ 12,399	$ (2,615)	$ 149,173	$ 428,101
Balance (in Shares) at Dec. 31, 2012	22,916,000	2,762,000