Securities - Amortized Cost and Fair Value (Details) $ in Thousands	9 Months Ended
Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Securities Available-for-Sale
Amortized Cost	$ 538,539	$ 470,719
Gross Unrealized Gains	4,498	383
Gross Unrealized Losses	(11,980)	(15,036)
Fair Value	531,057	456,066
Securities Held-to-Maturity
Amortized Cost		247,746
Gross Unrealized Gains		4,894
Gross Unrealized Losses		(965)
Fair Value		251,675
U.S. Treasury
Securities Available-for-Sale
Amortized Cost		1,509
Fair Value		1,509
U.S. government agencies
Securities Available-for-Sale
Amortized Cost	1,661	1,683
Gross Unrealized Losses	(158)	(127)
Fair Value	1,503	1,556
States and political subdivisions
Securities Available-for-Sale
Amortized Cost	21,489	30,341
Gross Unrealized Gains	765	285
Gross Unrealized Losses		(100)
Fair Value	22,254	30,526
Corporate bonds
Securities Available-for-Sale
Amortized Cost	10,958	30,157
Gross Unrealized Losses	(228)	(757)
Fair Value	10,730	29,400
Collateralized mortgage obligations
Securities Available-for-Sale
Amortized Cost	202,670	68,743
Gross Unrealized Gains	2,478	24
Gross Unrealized Losses	(758)	(1,847)
Fair Value	204,390	66,920
Securities Held-to-Maturity
Amortized Cost		211,241
Gross Unrealized Gains		3,302
Gross Unrealized Losses		(965)
Fair Value		213,578
Asset-backed securities
Securities Available-for-Sale
Amortized Cost	149,394	241,872
Gross Unrealized Gains	431	74
Gross Unrealized Losses	(9,652)	(10,038)
Fair Value	140,173	231,908
FFEL
Other disclosures
Asset-backed securities	$ 118,900
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	$ 12,800
Percentage of total added credit enhancement in the form of overcollaterization and/or subordination of outstanding principal	9.62
Collateralized loan obligations
Securities Available-for-Sale
Amortized Cost	$ 109,468	94,374
Gross Unrealized Losses	(1,184)	(2,123)
Fair Value	108,284	92,251
U.S. government agency mortgage-backed
Securities Available-for-Sale
Amortized Cost	42,899	2,040
Gross Unrealized Gains	824
Gross Unrealized Losses		(44)
Fair Value	$ 43,723	1,996
Securities Held-to-Maturity
Amortized Cost		36,505
Gross Unrealized Gains		1,592
Fair Value		$ 38,097

Reflects percentage of outstanding principal amount of loans guaranteed by US Department of Education.

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Investments in notes or bonds that are collateralized by a specific group of underlying assets owned by the issuer of the notes or bonds which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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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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Amount of assets pledged to secure a debt instrument.

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

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