Condensed 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, 2012	$ 1,139,525	$ 5,519	$ 651,148	$ 493,666	$ (10,536)	$ (272)
Balances, shares at Dec. 31, 2012	55,186
Stock-based compensation expense	4,846		4,846
Shares repurchased and retired, shares	(1,631)
Shares repurchased and retired, value	(30,673)	(163)	(17,573)	(12,937)
Stock options exercised, shares	666
Stock options exercised, value	10,405	67	10,338
Issuance of restricted shares, net of forfeitures, shares	13
Issuance of restricted shares, net of forfeitures, value	0	1	(1)
Restricted shares withheld for taxes, shares	(7)
Restricted shares withheld for taxes, value	(117)	(1)	(116)
Excess tax shortfall of stock-based compensation	(466)		(466)
Comprehensive income	44,233			43,670	563
Balances, value at Sep. 30, 2013	$ 1,167,753	$ 5,423	$ 648,176	$ 524,399	$ (9,973)	$ (272)
Balances, shares at Sep. 30, 2013	54,227