Securities - Amortized Cost and Fair Value of Securities Available for Sale and Held for Investment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities Available for Sale
Available for sale, amortized cost, total	$ 882,872	$ 953,720
Available for sale, gross unrealized gains	1,306	4,202
Available for sale, gross unrealized losses	(18,347)	(8,462)
Available for sale, fair value	865,831	949,460
Debt Securities Held to Maturity
Held to maturity, amortized cost	357,949	416,863
Held to maturity, gross unrealized gains	277	1,819
Held to maturity, gross unreazlied losses	(8,331)	(4,212)
Held to maturity, fair value	349,895	414,470
U.S. Treasury securities and obligations of U.S. Government Sponsored Entities
Debt Securities Available for Sale
Available for sale, amortized cost, total	7,200	9,475
Available for sale, gross unrealized gains	106	274
Available for sale, gross unrealized losses	(6)	(5)
Available for sale, fair value	7,300	9,744
Mortgage-backed securities and collateralized mortgage obligations of US Government Sponsored Entities
Debt Securities Available for Sale
Available for sale, amortized cost, total	567,753	560,396
Available for sale, gross unrealized gains	300	1,163
Available for sale, gross unrealized losses	(14,047)	(8,034)
Available for sale, fair value	554,006	553,525
Debt Securities Held to Maturity
Held to maturity, amortized cost	304,423	353,541
Held to maturity, gross unrealized gains	0	802
Held to maturity, gross unreazlied losses	(7,324)	(4,159)
Held to maturity, fair value	297,099	350,184
Private mortgage-backed securities and collateralized mortgage obligations
Debt Securities Available for Sale
Available for sale, amortized cost, total	55,569	75,152
Available for sale, gross unrealized gains	560	1,154
Available for sale, gross unrealized losses	(401)	(285)
Available for sale, fair value	55,728	76,021
Debt Securities Held to Maturity
Held to maturity, amortized cost	21,526	22,799
Held to maturity, gross unrealized gains	277	714
Held to maturity, gross unreazlied losses	(130)	(53)
Held to maturity, fair value	21,673	23,460
Collateralized loan obligations
Debt Securities Available for Sale
Available for sale, amortized cost, total	212,807	263,579
Available for sale, gross unrealized gains	1	798
Available for sale, gross unrealized losses	(3,442)	(68)
Available for sale, fair value	209,366	264,309
Debt Securities Held to Maturity
Held to maturity, amortized cost	32,000	40,523
Held to maturity, gross unrealized gains	0	303
Held to maturity, gross unreazlied losses	(877)	0
Held to maturity, fair value	31,123	40,826
Obligations of state and political subdivisions
Debt Securities Available for Sale
Available for sale, amortized cost, total	39,543	45,118
Available for sale, gross unrealized gains	339	813
Available for sale, gross unrealized losses	(451)	(70)
Available for sale, fair value	$ 39,431	$ 45,861

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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