Securities - Summary of Amortized Cost and Estimated Fair Value of Securities Available-for-Sale and Securities Held-to-Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Securities available-for-sale, Amortized Cost	$ 1,221,511	$ 1,262,688
Securities available-for-sale, Gross Unrealized Gains	1,658	10,397
Securities available-for-sale, Gross Unrealized Losses	35,917	16,022
Securities available-for-sale, Estimated Fair Value	1,187,252	1,257,063
Securities held-to-maturity, Amortized Cost	0	290
Securities held-to-maturity, Estimated Fair Value		311
U.S. Treasury Securities
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Securities available-for-sale, Amortized Cost	100,413	100,575
Securities available-for-sale, Gross Unrealized Losses	3,628	3,731
Securities available-for-sale, Estimated Fair Value	96,785	96,844
Obligations of U.S. Government Agencies
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Securities available-for-sale, Amortized Cost	60,975	80,552
Securities available-for-sale, Gross Unrealized Gains	316	738
Securities available-for-sale, Gross Unrealized Losses	284	66
Securities available-for-sale, Estimated Fair Value	61,007	81,224
Residential Pass-through \| Guaranteed by GNMA
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Securities available-for-sale, Amortized Cost	85,052	106,461
Securities available-for-sale, Gross Unrealized Gains	146	676
Securities available-for-sale, Gross Unrealized Losses	2,093	1,110
Securities available-for-sale, Estimated Fair Value	83,105	106,027
Residential Pass-through \| Issued by FNMA and FHLMC
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Securities available-for-sale, Amortized Cost	594,874	431,409
Securities available-for-sale, Gross Unrealized Gains	694	1,284
Securities available-for-sale, Gross Unrealized Losses	10,367	2,271
Securities available-for-sale, Estimated Fair Value	585,201	430,422
Other Residential Mortgage-Backed Securities
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Securities available-for-sale, Amortized Cost	36,339	47,379
Securities available-for-sale, Gross Unrealized Gains	8	97
Securities available-for-sale, Gross Unrealized Losses	1,178	1,084
Securities available-for-sale, Estimated Fair Value	35,169	46,392
Commercial Mortgage-Backed Securities
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Securities available-for-sale, Amortized Cost	114,383	76,201
Securities available-for-sale, Gross Unrealized Gains	287	63
Securities available-for-sale, Gross Unrealized Losses	5,255	4,069
Securities available-for-sale, Estimated Fair Value	109,415	72,195
Total MBS
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Securities available-for-sale, Amortized Cost	830,648	661,450
Securities available-for-sale, Gross Unrealized Gains	1,135	2,120
Securities available-for-sale, Gross Unrealized Losses	18,893	8,534
Securities available-for-sale, Estimated Fair Value	812,890	655,036
Obligations of States and Municipal Subdivisions
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Securities available-for-sale, Amortized Cost	229,475	420,111
Securities available-for-sale, Gross Unrealized Gains	207	7,539
Securities available-for-sale, Gross Unrealized Losses	13,112	3,691
Securities available-for-sale, Estimated Fair Value	$ 216,570	423,959
Securities held-to-maturity, Amortized Cost		290
Securities held-to-maturity, Gross Unrealized Gains		21
Securities held-to-maturity, Estimated Fair Value		$ 311

Schedule of available-for-sale securities and held-to-maturity.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

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This item represents the cost of debt and equity 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 after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Amount of accumulated unrealized gain on 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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