Borrowings (Long-Term Debt) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Notes and subordinated debt	$ 227,320,000	$ 227,320,000
Debt issuance cost on senior fixed-rate notes	(826,000)	(961,000)
Long-term debt	$ 225,767,000	$ 225,514,000
Long term debt, variable interest rate, percentage	4.55%	3.94%
London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate spread of LIBOR plus (as a percent)	2.95%
Long-term Debt [Member]
Debt Instrument [Line Items]
Discount on senior fixed-rate notes	$ (727,000)	$ (845,000)
Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate, percentage	4.375%
Notes and subordinated debt	$ 150,000,000	150,000,000
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Notes and subordinated debt	$ 77,320,000	$ 77,320,000

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after accumulated amortization, of debt discount.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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The percentage points added to the reference rate to compute the variable rate on the interest rate derivative.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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