Consolidated Statements Of Changes In Stockholder's Equity (USD $) In Thousands, except Share data	Common Stock [Member]	Additional Paid-In Capital [Member] USD ($)	Accumulated Other Comprehensive Income (Loss), Net Of Deferred Income Taxes [Member] USD ($)	Retained Earnings [Member] USD ($)	Total USD ($)
Balance, beginning of period at Mar. 31, 2013		$ 343,381	$ 171,653	$ 3,239,167
Balance, beginning of period, shares at Mar. 31, 2013	1,000
Share-based compensation plans		2,898
Net increase (decrease) during the period			(77,023)		(77,023)
Net income (loss)				85,262	85,262
Balance, end of period at Jun. 30, 2013		346,279	94,630	3,324,429	3,765,338
Balance, end of period, shares at Jun. 30, 2013	1,000
Balance, beginning of period at Dec. 31, 2012		340,223	184,867	2,953,516
Balance, beginning of period, shares at Dec. 31, 2012	1,000
Share-based compensation plans		6,056
Net increase (decrease) during the period			(90,237)		(90,237)
Net income (loss)				370,913	370,913
Balance, end of period at Jun. 30, 2013		346,279	94,630	3,324,429	3,765,338
Balance, end of period, shares at Jun. 30, 2013	1,000
Balance, beginning of period at Dec. 31, 2013		351,051	87,648	3,751,779	4,190,478
Balance, beginning of period, shares at Dec. 31, 2013	1,000				1,000
Share-based compensation plans		6,486
Net increase (decrease) during the period			42,480		42,480
Net income (loss)				244,640	244,640
Balance, end of period at Jun. 30, 2014		357,537	130,128	3,996,419	4,484,084
Balance, end of period, shares at Jun. 30, 2014	1,000				1,000
Balance, beginning of period at Mar. 31, 2014		354,445	102,678	3,838,245
Balance, beginning of period, shares at Mar. 31, 2014	1,000
Share-based compensation plans		3,092
Net increase (decrease) during the period			27,450		27,450
Net income (loss)				158,174	158,174
Balance, end of period at Jun. 30, 2014		$ 357,537	$ 130,128	$ 3,996,419	$ 4,484,084
Balance, end of period, shares at Jun. 30, 2014	1,000				1,000