Consolidated Statements Of Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Beginning of year at Dec. 31, 2011		$ 76,634	$ 538	$ 0	$ 1,780,311
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options		(2,492)	0
Share-based compensation expense	(370)	(168)	(538)
Tax benefit on sales of incentive stock options	86	86
Other comprehensive income, net of tax				0
Net income	116,911				116,911
Dividends paid to shareholders					(134,105)
End of year at Dec. 31, 2012	1,842,497	79,380	0	0	1,763,117
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options		(1,884)	(438)
Share-based compensation expense	(974)	(125)	(849)
Tax benefit on sales of incentive stock options	202	202
Other comprehensive income, net of tax				0
Net income	112,143				112,143
Dividends paid to shareholders					(134,776)
End of year at Dec. 31, 2013	1,822,486	81,591	411	0	1,740,484
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options		(6,824)	(577)
Share-based compensation expense	(4,112)	(142)	(3,970)
Tax benefit on sales of incentive stock options	148	148
Other comprehensive income, net of tax				0
Net income	177,949				177,949
Dividends paid to shareholders					(135,496)
End of year at Dec. 31, 2014	$ 1,875,446	$ 88,705	$ 3,804	$ 0	$ 1,782,937