Investment Securities - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 584,382	$ 745,328
Gross Unrealized Gains	4,275	805
Gross Unrealized Losses	(538)	(8,691)
Fair Value	588,119	737,442
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	100	200,026
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	(13)
Fair Value	101	200,013
Obligations of the U.S. government and agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	192,524	198,604
Gross Unrealized Gains	374	107
Gross Unrealized Losses	(99)	(2,856)
Fair Value	192,799	195,855
Obligations of state and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,862	11,372
Gross Unrealized Gains	10	3
Gross Unrealized Losses	(2)	(43)
Fair Value	6,870	11,332
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	345,611	294,076
Gross Unrealized Gains	3,597	554
Gross Unrealized Losses	(233)	(4,740)
Fair Value	348,975	289,890
Collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	38,635	40,150
Gross Unrealized Gains	293	141
Gross Unrealized Losses	(204)	(1,039)
Fair Value	38,724	39,252
Other investment securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	650	1,100
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 650	$ 1,100

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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Amount, before tax, of unrealized loss 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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Amount 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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