Debt Securities Available for Sale - Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,095,422	$ 1,049,932
Gross Unrealized Gains	22,137	2,994
Gross Unrealized (Losses)	(1,654)	(20,058)
Debt securities available for sale, at fair value	1,115,905	1,032,868
U.S. government and agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	44,532	54,821
Gross Unrealized Gains	621	53
Gross Unrealized (Losses)	(22)	(717)
Debt securities available for sale, at fair value	45,131	54,157
Mortgage-backed securities and collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	981,205	934,631
Gross Unrealized Gains	20,742	2,812
Gross Unrealized (Losses)	(504)	(17,436)
Debt securities available for sale, at fair value	1,001,443	920,007
Municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	190	987
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	0	0
Debt securities available for sale, at fair value	190	987
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	64,495	54,493
Gross Unrealized Gains	774	129
Gross Unrealized (Losses)	(669)	(1,155)
Debt securities available for sale, at fair value	64,600	53,467
Trust preferred securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,000	5,000
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(459)	(750)
Debt securities available for sale, at fair value	$ 4,541	$ 4,250

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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