Securities - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Amortized cost and fair value of securities available for sale
Amortized Cost	$ 1,222,123	$ 1,264,529
Gross Unrealized Gains	20,591	4,517
Gross Unrealized Losses	(4,137)	(18,269)
Fair Value	1,238,577	1,250,777
U.S. Treasury securities
Amortized cost and fair value of securities available for sale
Amortized Cost	498
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	498
Obligations of other U.S. Government agencies and corporations
Amortized cost and fair value of securities available for sale
Amortized Cost	2,523	2,536
Gross Unrealized Gains	18	13
Gross Unrealized Losses	(4)	(38)
Fair Value	2,537	2,511
Obligations of states and political subdivisions
Amortized cost and fair value of securities available for sale
Amortized Cost	211,559	200,798
Gross Unrealized Gains	5,585	3,038
Gross Unrealized Losses	(156)	(567)
Fair Value	216,988	203,269
Trust preferred securities
Amortized cost and fair value of securities available for sale
Amortized Cost	12,160	12,359
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2,298)	(1,726)
Fair Value	9,862	10,633
Other debt securities
Amortized cost and fair value of securities available for sale
Amortized Cost	46,739	44,046
Gross Unrealized Gains	1,513	192
Gross Unrealized Losses	(3)	(311)
Fair Value	48,249	43,927
Government agency mortgage backed securities \| Residential mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	658,830	621,690
Gross Unrealized Gains	8,723	719
Gross Unrealized Losses	(1,386)	(9,126)
Fair Value	666,167	613,283
Government agency mortgage backed securities \| Commercial mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	26,794	21,957
Gross Unrealized Gains	874	257
Gross Unrealized Losses	(2)	(384)
Fair Value	27,666	21,830
Government agency collateralized mortgage obligations \| Residential mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	189,332	332,697
Gross Unrealized Gains	2,123	274
Gross Unrealized Losses	(268)	(5,982)
Fair Value	191,187	326,989
Government agency collateralized mortgage obligations \| Commercial mortgage backed securities:
Amortized cost and fair value of securities available for sale
Amortized Cost	73,688	28,446
Gross Unrealized Gains	1,755	24
Gross Unrealized Losses	(20)	(135)
Fair Value	$ 75,423	$ 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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Amortized cost of 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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