Restatement of Previously Issued Condensed Consolidated Financial Statements (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Net income	$ 71,971	$ 70,575	$ 134,753	$ 186,523
Other comprehensive income, net of income taxes	(37,364)	109,684	(361,381)	202,443
Accumulated other comprehensive income	274,318	672,425	274,318	672,425	311,682	635,699	562,741	469,982
Retained earnings	766,342	700,535	766,342	700,535		722,525
Total	1,820,771	2,150,146	1,820,771	2,150,146		2,136,297		1,914,073
As previously reported
Net income		63,271		175,313
Other comprehensive income, net of income taxes		113,407		207,677
Accumulated other comprehensive income		677,659		677,659
Retained earnings		689,325		689,325
Total		2,144,170		2,144,170
Accounting for forward settling to be announced (TBA) security transactions | Adjustments
Net income		7,304		11,210
Other comprehensive income, net of income taxes		(3,723)		(5,234)
Accumulated other comprehensive income		(5,234)		(5,234)
Retained earnings		11,210		11,210
Total		$ 5,976		$ 5,976