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Securities - Amortized Cost and Fair Value (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Securities Available-for-Sale
Amortized Cost	$ 620,435		$ 545,433
Gross Unrealized Gains	1,256		1,011
Gross Unrealized Losses	(10,637)		(14,606)
Fair Value	611,054		531,838
Other disclosures
Purchases	154,653	$ 88,005
Sales	64,388	$ 35,574
U.S. government agencies
Securities Available-for-Sale
Amortized Cost			42,511
Gross Unrealized Losses			(977)
Fair Value			41,534
States and political subdivisions
Securities Available-for-Sale
Amortized Cost	219,223		68,718
Gross Unrealized Gains	856		258
Gross Unrealized Losses	(572)		(273)
Fair Value	219,507		68,703
Corporate bonds
Securities Available-for-Sale
Amortized Cost	12,807		10,957
Gross Unrealized Gains	47		9
Gross Unrealized Losses	(314)		(336)
Fair Value	12,540		10,630
Collateralized mortgage obligations
Securities Available-for-Sale
Amortized Cost	110,805		174,352
Gross Unrealized Gains	119		374
Gross Unrealized Losses	(2,600)		(3,799)
Fair Value	108,324		170,927
Asset-backed securities
Securities Available-for-Sale
Amortized Cost	146,103		146,391
Gross Unrealized Gains	196		341
Gross Unrealized Losses	(6,413)		(8,325)
Fair Value	139,886		138,407
FFEL
Other disclosures
Asset-backed securities	$ 119,000
Percentage of outstanding principal amount of loans guaranteed by US Department of Education	97.00
Total added credit enhancement in the form of overcollaterization and/or subordination of outstanding principal	$ 13,000
Percentage of total added credit enhancement in the form of overcollaterization and/or subordination of outstanding principal	10.01
Collateralized loan obligations
Securities Available-for-Sale
Amortized Cost	$ 92,564		102,504
Gross Unrealized Gains	21		29
Gross Unrealized Losses	(346)		(896)
Fair Value	92,239		$ 101,637
U.S. government agency mortgage-backed
Securities Available-for-Sale
Amortized Cost	38,933
Gross Unrealized Gains	17
Gross Unrealized Losses	(392)
Fair Value	$ 38,558

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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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