Investments (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 106,602	$ 773,925
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(882)	(33,356)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	173,724	5,032
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(2,720)	(189)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	280,326	778,957
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(3,602)	(33,545)
Government agency and government-sponsored enterprise pass through securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	10,711	148,662
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(13)	(2,767)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	27,100	32
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(359)	(1)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	37,811	148,694
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(372)	(2,768)
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	23,908	179,938
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(73)	(4,486)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	40,652	4,383
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(1,007)	(98)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	64,560	184,321
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(1,080)	(4,584)
Covered private label collateralized mortgage obligation [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	0	1,640
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	(60)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	1,000	617
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(95)	(90)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	1,000	2,257
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(95)	(150)
Other Private Label Collateralized Mortgage Obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	1,618
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(93)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	1,618
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(93)
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	11,854	337,208
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(66)	(24,273)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	84,822
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(1,216)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	96,676	337,208
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(1,282)	(24,273)
Corporate Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	52,071	72,636
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(547)	(1,483)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	10,131	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(15)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	62,202	72,636
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(562)	(1,483)
US Government-sponsored Enterprises Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss		9,872
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		(174)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss		9,872
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		(174)
Other securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	6,440	23,969
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(90)	(113)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	10,019	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(28)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	16,459	23,969
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ (118)	$ (113)