Securities - Schedule of Securities with Unrealized Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Available-for-sale securities
Fair Value, Less than 12 Months	$ 114,404	$ 111,648
Unrealized Losses, Less than 12 Months	706	886
Fair Value, 12 Months or Longer	359,423	1,109,535
Unrealized Losses, 12 Months or Longer	4,468	31,256
Fair Value	473,827	1,221,183
Unrealized Losses	5,174	32,142
Held-to-maturity debt securities
Fair Value, Less than 12 Months		13,107
Unrealized Losses, Less than 12 Months		33
Fair Value, 12 Months or Longer		125,128
Unrealized Losses, 12 Months or Longer		1,189
Fair Value		138,235
Unrealized Losses		1,222
Obligations of U.S. Government sponsored entities
Available-for-sale securities
Fair Value, Less than 12 Months	9,451	21,660
Unrealized Losses, Less than 12 Months	49	183
Fair Value, 12 Months or Longer	8,540	449,141
Unrealized Losses, 12 Months or Longer	14	7,370
Fair Value	17,991	470,801
Unrealized Losses	63	7,553
Held-to-maturity debt securities
Fair Value, Less than 12 Months		4,980
Unrealized Losses, Less than 12 Months		9
Fair Value, 12 Months or Longer		125,128
Unrealized Losses, 12 Months or Longer		1,189
Fair Value		130,108
Unrealized Losses		1,198
Obligations of U.S. states and political subdivisions
Available-for-sale securities
Fair Value, Less than 12 Months	5,761	11,971
Unrealized Losses, Less than 12 Months	45	19
Fair Value, 12 Months or Longer	2,295	49,756
Unrealized Losses, 12 Months or Longer	15	914
Fair Value	8,056	61,727
Unrealized Losses	60	933
Held-to-maturity debt securities
Fair Value, Less than 12 Months		8,127
Unrealized Losses, Less than 12 Months		24
Fair Value, 12 Months or Longer		0
Unrealized Losses, 12 Months or Longer		0
Fair Value		8,127
Unrealized Losses		24
U.S. Government agencies
Available-for-sale securities
Fair Value, Less than 12 Months	57,136	16,854
Unrealized Losses, Less than 12 Months	336	22
Fair Value, 12 Months or Longer	49,624	96,247
Unrealized Losses, 12 Months or Longer	983	3,710
Fair Value	106,760	113,101
Unrealized Losses	1,319	3,732
U.S. Government sponsored entities
Available-for-sale securities
Fair Value, Less than 12 Months	42,056	61,163
Unrealized Losses, Less than 12 Months	276	662
Fair Value, 12 Months or Longer	296,532	512,216
Unrealized Losses, 12 Months or Longer	3,388	18,937
Fair Value	338,588	573,379
Unrealized Losses	3,664	19,599
U.S. corporate debt securities
Available-for-sale securities
Fair Value, Less than 12 Months	0	0
Unrealized Losses, Less than 12 Months	0	0
Fair Value, 12 Months or Longer	2,432	2,175
Unrealized Losses, 12 Months or Longer	68	325
Fair Value	2,432	2,175
Unrealized Losses	$ 68	$ 325

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