Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Net income	$ 354,124	$ 289,824	$ 248,294
Other Comprehensive Income (Loss), before Tax [Abstract]
Net change in unrealized gain (loss)	66,197	47,287	185,463
Other-than-temporary impairment losses recognized in earnings	7,351	23,507	27,809
Reclassification adjustment for net (gains) losses realized and included in earnings	(33,392)	(33,840)	(21,618)
Amortization of unrealized gain on investment securities transferred from available for sale	(6,601)	(1,357)	0
Other comprehensive income before income taxes	33,555	35,597	191,654
Other Comprehensive Income (Loss), Tax	(12,614)	(14,457)	(73,075)
Other Comprehensive Income (Loss), Net of Tax	20,941	21,140	118,579
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	375,065	310,964	366,873
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest	2,933	3,949	1,540
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 372,132	$ 307,015	$ 365,333