Investments Investment Securities in Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2018 USD ($) securities		Dec. 31, 2017 USD ($) securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 480,364		$ 378,406
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(8,248)		(2,463)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	495,916		495,297
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(23,922)		(14,708)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	976,280		873,703
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ 32,170		$ 17,171
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	258		208
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 55,189		$ 59,218
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,505)		(534)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	13,698		14,563
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(417)		(261)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	68,887		73,781
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (1,922)		$ (795)
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	16		16
US Government and Government Agencies and Authorities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 14,844		$ 14,902
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(138)		(79)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	18,963		19,397
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(1,115)		(754)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	33,807		34,299
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ 1,253		$ 833
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	6		6
US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 223,047		$ 220,275
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(3,391)		(1,350)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	57,516		38,273
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(2,038)		(1,272)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	280,563		258,548
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ 5,429		$ 2,622
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	41		36
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 141,784		$ 46,112
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(1,811)		(131)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	49,429		50,842
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(2,262)		(1,017)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	191,213		96,954
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ 4,073		$ 1,148
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	102		63
Mortgage Backed Securities, Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 100,689	[1]	$ 97,117	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(2,908)	[1]	(903)	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	370,008	[1]	386,785	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(18,507)	[1]	(11,665)	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	470,697	[1]	483,902	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ 21,415	[1]	$ 12,568	[2]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	109	[1]	103	[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 55,189	[1]	$ 59,218	[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,505)	[1]	(534)	[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	13,698	[1]	14,563	[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(417)	[1]	(261)	[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	68,887	[1]	73,781	[2]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (1,922)	[1]	$ (795)	[2]
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	16	[1]	16	[2]

[1] All mortgage-backed securities are guaranteed by U.S. government agencies or government-sponsored entities.

[2] All mortgage-backed securities are guaranteed by U.S. government agencies or government-sponsored entities.