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, 2010		$ 74,188	$ 78	$ (740)	$ 1,721,289
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options		1,951	0
Share-based compensation expense	899	439	460
Tax benefit on sales of incentive stock options	56	56
Other comprehensive income, net of tax				740
Net income	191,164				191,164
Dividends paid to shareholders					(132,142)
End of year at Dec. 31, 2011	1,857,483	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