Securities - Amortized Cost and Fair Value of Securities Available for Sale and Held for Investment (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt securities available for sale
Available for sale, amortized cost, total	$ 907,178	$ 882,872
Available for sale, gross unrealized gains	15,573	1,306
Available for sale, gross unrealized losses	(1,940)	(18,347)
Available for sale, fair value	920,811	865,831
Debt securities held to maturity
Held to maturity, amortized cost, total	273,644	357,949
Held to maturity, gross unrealized gains	3,930	277
Held to maturity, gross unrealized losses	(1,505)	(8,331)
Held to maturity, fair value	276,069	349,895
U.S. Treasury securities and obligations of U.S. government agencies
Debt securities available for sale
Available for sale, amortized cost, total	10,206	7,200
Available for sale, gross unrealized gains	319	106
Available for sale, gross unrealized losses	(1)	(6)
Available for sale, fair value	10,524	7,300
Mortgage-backed securities and collateralized mortgage obligations of U.S. government sponsored entities
Debt securities available for sale
Available for sale, amortized cost, total	562,270	567,753
Available for sale, gross unrealized gains	12,096	300
Available for sale, gross unrealized losses	(520)	(14,047)
Available for sale, fair value	573,846	554,006
Debt securities held to maturity
Held to maturity, amortized cost, total	273,644	304,423
Held to maturity, gross unrealized gains	3,930	0
Held to maturity, gross unrealized losses	(1,505)	(7,324)
Held to maturity, fair value	276,069	297,099
Private mortgage-backed securities and collateralized mortgage obligations
Debt securities available for sale
Available for sale, amortized cost, total	60,809	55,569
Available for sale, gross unrealized gains	1,808	560
Available for sale, gross unrealized losses	(17)	(401)
Available for sale, fair value	62,600	55,728
Debt securities held to maturity
Held to maturity, amortized cost, total		21,526
Held to maturity, gross unrealized gains		277
Held to maturity, gross unrealized losses		(130)
Held to maturity, fair value	0	21,673
Collateralized loan obligations
Debt securities available for sale
Available for sale, amortized cost, total	241,387	212,807
Available for sale, gross unrealized gains	1	1
Available for sale, gross unrealized losses	(1,402)	(3,442)
Available for sale, fair value	239,986	209,366
Debt securities held to maturity
Held to maturity, amortized cost, total		32,000
Held to maturity, gross unrealized gains		0
Held to maturity, gross unrealized losses		(877)
Held to maturity, fair value		31,123
Obligations of state and political subdivisions
Debt securities available for sale
Available for sale, amortized cost, total	32,506	39,543
Available for sale, gross unrealized gains	1,349	339
Available for sale, gross unrealized losses	0	(451)
Available for sale, fair value	$ 33,855	$ 39,431

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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