Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Total
Balance at December 31 at Dec. 31, 2011	$ 480	$ 863,128	$ 12,927	$ (7,240)	$ (659)	$ 868,636
Balance at December 31 (in Shares) at Dec. 31, 2011	48,017,108				(59,912)
Net Income			62,699			62,699
Other Comprehensive Income (Loss), Net Of Tax				12,078		12,078
Total comprehensive income						74,777
Shares issued upon exercise of stock options and awards of restricted stock	8	16,616				16,624
Shares issued upon exercise of stock options and awards of restricted stock (in Shares)	752,855
Dividends declared			(96,915)			(96,915)
Stock-based compensation expense		16,225				16,225
Reversal of uncertain tax positions due to statute of limitations		1,551				1,551
Retirement of treasury stock	(1)	(659)			659	(1)
Retirement of treasury stock (in Shares)	(62,230)				62,230
Forfeiture of restricted stock (in Shares)	(8,976)				(2,318)
Balance at December 31 at Dec. 31, 2012	487	896,861	(21,289)	4,838		880,897
Balance at December 31 (in Shares) at Dec. 31, 2012	48,698,757
Net Income			314,385			314,385
Other Comprehensive Income (Loss), Net Of Tax				6,737		6,737
Total comprehensive income						321,122
Shares issued upon exercise of stock options and awards of restricted stock	2	5,116				5,118
Shares issued upon exercise of stock options and awards of restricted stock (in Shares)	178,737
Stock-based compensation expense		9,652				9,652
Forfeiture of restricted stock	(1)	1
Forfeiture of restricted stock (in Shares)	(88,607)
Net income tax deficiency from share-based compensation		(3,540)				(3,540)
Balance at December 31 at Dec. 31, 2013	488	908,090	293,096	11,575		1,213,249
Balance at December 31 (in Shares) at Dec. 31, 2013	48,788,887
Net Income			63,143			63,143
Other Comprehensive Income (Loss), Net Of Tax				(1,120)		(1,120)
Total comprehensive income						62,023
Shares issued upon exercise of stock options and awards of restricted stock	0	374				374
Shares issued upon exercise of stock options and awards of restricted stock (in Shares)	57,021
Dividends declared			(48,820)			(48,820)
Stock-based compensation expense		5,979				5,979
Forfeiture of restricted stock	0	0				0
Forfeiture of restricted stock (in Shares)	(14,269)
Net income tax deficiency from share-based compensation		(4,469)				(4,469)
Balance at December 31 at Dec. 31, 2014	$ 488	$ 909,974	$ 307,419	$ 10,455		$ 1,228,336
Balance at December 31 (in Shares) at Dec. 31, 2014	48,831,639