Consolidated Statements Of Shareholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Additional Paid In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Stock [Member]
Balances, value at Dec. 31, 2011	$ 1,115,748	$ 5,779	$ 674,498	$ 449,193	$ (13,450)	$ (272)
Balances, shares at Dec. 31, 2011	57,791
Stock-based compensation expense	6,270		6,270
Shares repurchased and retired, shares	(3,224)
Shares repurchased and retired, value	(47,106)	(322)	(34,650)	(12,134)
Stock options exercised, shares	375
Stock options exercised, value	4,657	38	4,619
Issuance of restricted shares, net of forfeitures, shares	244
Issuance of restricted shares, net of forfeitures, value		24	(24)
Excess tax benefit (shortfall) of stock-based compensation	435		435
Comprehensive income	59,521			56,607	2,914
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	6,267		6,267
Shares repurchased and retired, shares	(2,093)
Shares repurchased and retired, value	(41,168)	(209)	(22,556)	(18,403)
Stock options exercised, shares	713
Stock options exercised, value	11,203	71	11,132
Issuance of restricted shares, net of forfeitures, shares	27
Issuance of restricted shares, net of forfeitures, value		3	(3)
Restricted shares withheld for taxes, shares	(8)
Restricted shares withheld for taxes	(142)	(1)	(141)
Excess tax benefit (shortfall) of stock-based compensation	(1,253)		(1,253)
Comprehensive income	112,601			111,159	1,442
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
Stock-based compensation expense	7,213		7,213
Shares repurchased and retired, shares	(1,861)
Shares repurchased and retired, value	(43,800)	(186)	(20,250)	(23,364)
Stock options exercised, shares	940
Stock options exercised, value	18,867	94	18,773
Issuance of restricted shares, net of forfeitures, shares	103
Issuance of restricted shares, net of forfeitures, value		10	(10)
Restricted shares withheld for taxes, shares	(13)
Restricted shares withheld for taxes	(309)	(1)	(308)
Excess tax benefit (shortfall) of stock-based compensation	(25)		(25)
Cancellation of treasury shares			(272)			272
Comprehensive income	82,061			82,442	(381)
Balances, value at Dec. 31, 2014	$ 1,291,040	$ 5,300	$ 649,715	$ 645,500	$ (9,475)	$ 0
Balances, shares at Dec. 31, 2014	52,994