Consolidated Statements Of Shareholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Additional Paid In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]
Balances, value at Dec. 31, 2013	$ 1,227,033	$ 5,383	$ 644,594	$ 586,422	$ (9,094)	$ (272)
Balances, shares at Dec. 31, 2013	53,825	53,825
Stock-based compensation expense	4,217		4,217
Shares repurchased and retired, shares		(509)
Shares repurchased and retired, value	(11,895)	(51)	(5,524)	(6,320)
Stock options exercised, shares	567	567
Stock options exercised, value	10,768	56	10,712
Issuance of restricted shares, net of forfeitures, shares		89
Issuance of restricted shares, net of forfeitures, value	0	9	(9)
Restricted shares withheld for taxes, shares		(13)
Restricted shares withheld for taxes	(309)	(1)	(308)
Excess tax benefit of stock-based compensation	171		171
Comprehensive income	40,873			41,275	(402)
Balances, value at Jun. 30, 2014	$ 1,270,858	$ 5,396	$ 653,853	$ 621,377	$ (9,496)	$ (272)
Balances, shares at Jun. 30, 2014	53,959	53,959