Securities - Amortized Cost and Fair Value of Securities Available for Sale and Held for Investment (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt securities available for sale
Available for sale, amortized cost, total	$ 882,557	$ 882,872
Available for sale, gross unrealized gains	3,473	1,306
Available for sale, gross unrealized losses	(8,481)	(18,347)
Available for sale, fair value	877,549	865,831
Debt securities held to maturity
Held to maturity, amortized cost, total	295,485	357,949
Held to maturity, gross unrealized gains	356	277
Held to maturity, gross unrealized losses	(4,501)	(8,331)
Held to maturity, fair value	291,340	349,895
U.S. Treasury securities and obligations of U.S. Government Sponsored Entities
Debt securities available for sale
Available for sale, amortized cost, total	6,296	7,200
Available for sale, gross unrealized gains	105	106
Available for sale, gross unrealized losses	(4)	(6)
Available for sale, fair value	6,397	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	528,404	567,753
Available for sale, gross unrealized gains	1,777	300
Available for sale, gross unrealized losses	(6,228)	(14,047)
Available for sale, fair value	523,953	554,006
Debt securities held to maturity
Held to maturity, amortized cost, total	295,485	304,423
Held to maturity, gross unrealized gains	356	0
Held to maturity, gross unrealized losses	(4,501)	(7,324)
Held to maturity, fair value	291,340	297,099
Private mortgage-backed securities and collateralized mortgage obligations
Debt securities available for sale
Available for sale, amortized cost, total	67,206	55,569
Available for sale, gross unrealized gains	968	560
Available for sale, gross unrealized losses	(239)	(401)
Available for sale, fair value	67,935	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	243,546	212,807
Available for sale, gross unrealized gains	2	1
Available for sale, gross unrealized losses	(1,809)	(3,442)
Available for sale, fair value	241,739	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	37,105	39,543
Available for sale, gross unrealized gains	621	339
Available for sale, gross unrealized losses	(201)	(451)
Available for sale, fair value	$ 37,525	$ 39,431

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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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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 of accumulated unrealized loss 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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