Investments (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 150,881	$ 106,602
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(1,866)	(882)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	74,198	173,724
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(1,545)	(2,720)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	225,079	280,326
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(3,411)	(3,602)
Government agency and government-sponsored enterprise pass through securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	5,031	10,711
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(42)	(13)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	10,085	27,100
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(89)	(359)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	15,116	37,811
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(131)	(372)
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	0	23,908
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	(73)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	14,403	40,652
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(451)	(1,007)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	14,403	64,560
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(451)	(1,080)
Covered private label collateralized mortgage obligation [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	726	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(6)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	643	1,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(60)	(95)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	1,369	1,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(66)	(95)
Other Private Label Collateralized Mortgage Obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	1,206	1,618
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(46)	(93)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	360	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(1)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	1,566	1,618
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(47)	(93)
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	112,361	11,854
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(1,277)	(66)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	38,687	84,822
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(922)	(1,216)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	151,048	96,676
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(2,199)	(1,282)
Corporate Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	25,104	52,071
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(423)	(547)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	10,131
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	(15)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	25,104	62,202
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(423)	(562)
Other securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	6,453	6,440
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(72)	(90)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	10,020	10,019
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(22)	(28)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	16,473	16,459
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ (94)	$ (118)