Investments (Details 2) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	$ 8,978	$ 882
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(451,209)	(106,602)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	2,579	2,720
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(73,592)	(173,724)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	11,557	3,602
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(524,801)	(280,326)
Government agency and government-sponsored enterprise pass through securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	92	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(4,952)	(10,711)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	158	359
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(9,707)	(27,100)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	250	372
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(14,659)	(37,811)
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	51	73
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(21,528)	(23,908)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	715	1,007
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(14,145)	(40,652)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	766	1,080
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(35,673)	(64,560)
Covered private label collateralized mortgage obligation [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	27	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(1,126)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	58	95
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(626)	(1,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	85	95
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(1,752)	(1,000)
Other Private Label Collateralized Mortgage Obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	39	93
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(2,188)	(1,618)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	4	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(428)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	43	93
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(2,616)	(1,618)
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	7,998	66
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(344,761)	(11,854)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	1,639	1,216
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(38,651)	(84,822)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	9,637	1,282
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(383,412)	(96,676)
Corporate Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	371	547
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(25,104)	(52,071)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	15
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	(10,131)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	371	562
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(25,104)	(62,202)
Collateralized Loan Obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	288
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(39,184)
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	288
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	(39,184)
Other securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	112	90
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	(12,366)	(6,440)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	5	28
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	(10,035)	(10,019)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss	117	118
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ (22,401)	$ (16,459)