Securities - Amortized Cost and Fair Value of Securities Available for Sale and Held for Investment (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt securities available-for-sale
Available for sale, amortized cost, total	$ 904,022	$ 940,765
Available for sale, gross unrealized gains	28,464	8,764
Available for sale, gross unrealized losses	(22,175)	(2,674)
Available for sale, fair value	910,311	946,855
Debt securities held-to-maturity
Held to maturity, amortized cost, total	252,373	261,369
Held to maturity, gross unrealized gains	9,447	2,717
Held to maturity, gross unrealized losses	(602)	(1,873)
Held to maturity, fair value	261,218	262,213
U.S. Treasury securities and obligations of U.S. government agencies
Debt securities available-for-sale
Available for sale, amortized cost, total	9,296	9,914
Available for sale, gross unrealized gains	287	204
Available for sale, gross unrealized losses	0	(4)
Available for sale, fair value	9,583	10,114
Mortgage-backed securities and collateralized mortgage obligations of U.S. government sponsored entities
Debt securities available-for-sale
Available for sale, amortized cost, total	608,711	604,934
Available for sale, gross unrealized gains	26,760	5,784
Available for sale, gross unrealized losses	(252)	(1,511)
Available for sale, fair value	635,219	609,207
Debt securities held-to-maturity
Held to maturity, amortized cost, total	252,373	261,369
Held to maturity, gross unrealized gains	9,447	2,717
Held to maturity, gross unrealized losses	(602)	(1,873)
Held to maturity, fair value	261,218	262,213
Private mortgage-backed securities and collateralized mortgage obligations
Debt securities available-for-sale
Available for sale, amortized cost, total	52,868	56,005
Available for sale, gross unrealized gains	111	1,561
Available for sale, gross unrealized losses	(2,410)	(5)
Available for sale, fair value	50,569	57,561
Debt securities held-to-maturity
Held to maturity, fair value	0
Collateralized loan obligations
Debt securities available-for-sale
Available for sale, amortized cost, total	205,238	239,364
Available for sale, gross unrealized gains	0	7
Available for sale, gross unrealized losses	(19,509)	(1,153)
Available for sale, fair value	185,729	238,218
Debt securities held-to-maturity
Held to maturity, fair value	0
Obligations of state and political subdivisions
Debt securities available-for-sale
Available for sale, amortized cost, total	27,909	30,548
Available for sale, gross unrealized gains	1,306	1,208
Available for sale, gross unrealized losses	(4)	(1)
Available for sale, fair value	$ 29,211	$ 31,755

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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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Amount, before other-than-temporary impairment (OTTI) accretion, of investment in debt securities measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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