Debt Securities Available for Sale - Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,079,469	$ 1,086,143
Gross Unrealized Gains	40,727	14,248
Gross Unrealized (Losses)	(3,779)	(2,055)
Debt securities available for sale, at fair value	1,116,417	1,098,336
U.S. government and agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	40,930	42,081
Gross Unrealized Gains	1,283	321
Gross Unrealized (Losses)	0	(16)
Debt securities available for sale, at fair value	42,213	42,386
Mortgage-backed securities and collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	963,977	968,165
Gross Unrealized Gains	38,878	12,981
Gross Unrealized (Losses)	(817)	(1,265)
Debt securities available for sale, at fair value	1,002,038	979,881
Municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	956	2,284
Gross Unrealized Gains	3	1
Gross Unrealized (Losses)	0	(1)
Debt securities available for sale, at fair value	959	2,284
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	68,606	68,613
Gross Unrealized Gains	563	945
Gross Unrealized (Losses)	(2,044)	(378)
Debt securities available for sale, at fair value	67,125	69,180
Trust preferred securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,000	5,000
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(918)	(395)
Debt securities available for sale, at fair value	$ 4,082	$ 4,605

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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