Securities - Amortized Cost and Fair Value, Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Amortized Cost	$ 1,276,871	$ 1,264,529
Gross Unrealized Gains	18,620	4,517
Gross Unrealized Losses	(4,878)	(18,269)
Fair Value	1,290,613	1,250,777
U.S. Treasury securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	498
Gross Unrealized Gains	1
Gross Unrealized Losses	0
Fair Value	499
Obligations of other U.S. Government agencies and corporations
Cash and Cash Equivalents [Line Items]
Amortized Cost	2,518	2,536
Gross Unrealized Gains	16	13
Gross Unrealized Losses	(3)	(38)
Fair Value	2,531	2,511
Obligations of states and political subdivisions
Cash and Cash Equivalents [Line Items]
Amortized Cost	218,362	200,798
Gross Unrealized Gains	5,134	3,038
Gross Unrealized Losses	(365)	(567)
Fair Value	223,131	203,269
Trust preferred securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	12,153	12,359
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2,167)	(1,726)
Fair Value	9,986	10,633
Other debt securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	55,364	44,046
Gross Unrealized Gains	1,133	192
Gross Unrealized Losses	(132)	(311)
Fair Value	56,365	43,927
Government agency mortgage backed securities \| Residential mortgage backed securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	708,970	621,690
Gross Unrealized Gains	8,951	719
Gross Unrealized Losses	(1,816)	(9,126)
Fair Value	716,105	613,283
Government agency mortgage backed securities \| Commercial mortgage backed securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	30,372	21,957
Gross Unrealized Gains	659	257
Gross Unrealized Losses	(24)	(384)
Fair Value	31,007	21,830
Government agency collateralized mortgage obligations \| Residential mortgage backed securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	172,178	332,697
Gross Unrealized Gains	1,322	274
Gross Unrealized Losses	(262)	(5,982)
Fair Value	173,238	326,989
Government agency collateralized mortgage obligations \| Commercial mortgage backed securities
Cash and Cash Equivalents [Line Items]
Amortized Cost	76,456	28,446
Gross Unrealized Gains	1,404	24
Gross Unrealized Losses	(109)	(135)
Fair Value	$ 77,751	$ 28,335

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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