Statements of Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (loss) [Member]	Total Equity
Balance at Dec. 31, 2011		$ 2,500	$ 882,670	$ (25,305)	$ 160,712	$ 1,020,577
Affiliated asset transfers	16,396	0	10,666		0	10,666
Distribution to parent	248,000	0		(248,000)	0	(248,000)
Comprehensive income:
Net income	444,947	0	0	444,947	0	444,947
Other comprehensive income (loss), net of tax	5,548	0	0	0	5,548	5,548
Total comprehensive income (loss)						450,495
Balance at Sep. 30, 2012		2,500	893,336	171,642	166,260	1,233,738
Balance at Dec. 31, 2012		2,500	893,336	200,754	147,287	1,243,877
Affiliated asset transfers	12,439	0	8,086	0	0	8,086
Distribution to parent	184,000	0	0	(184,000)	0	(184,000)
Comprehensive income:
Net income	691,354	0	0	691,354	0	691,354
Other comprehensive income (loss), net of tax	(67,743)	0	0	0	(67,743)	(67,743)
Total comprehensive income (loss)						623,611
Balance at Sep. 30, 2013		$ 2,500	$ 901,422	$ 708,108	$ 79,544	$ 1,691,574