Fair Value Measurements Fair Value Measurements, Financial Instruments Measured On a Recurring Basis, Quantitative Information (Details) - Fair Value, Measurements, Recurring [Member] - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	9 Months Ended				12 Months Ended
	Sep. 30, 2017		Sep. 30, 2016		Dec. 31, 2016
Available-for-sale securities [Member] | Municipal and other tax-exempt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Asset, Par Value	$ 5,095		$ 6,195		$ 6,195
Fair Value Inputs, Asset, Amortized Cost/Unpaid Principal Balance	5,067		6,162		6,163
Fair Value Inputs, Asset, Fair Value	$ 4,785		$ 5,713		$ 5,789
Fair Value Measurements, Valuation Techniques	Discounted cash flows	[1]	Discounted cash flows	[2]	Discounted cash flows	[3]
Fair Value Measurements, Significant Unobservable Input	Interest rate spread		Interest rate spread		Interest rate spread
Fair Value Inputs, Assets, Discount Rate, Minimum	6.05%	[4]	5.60%	[5]	5.91%	[6]
Fair Value Inputs, Assets, Discount Rate, Maximum	6.05%	[4]	5.90%	[5]	6.21%	[6]
Fair Value Inputs, Assets, Discount Rate, Weighted Average	6.05%	[4]	5.85%	[5]	6.16%	[6]
Fair Value Inputs, Assets, Fair Value As Percentage of Par Value, Minimum	92.25%	[7]	90.00%	[8]	90.00%	[9]
Fair Value Inputs, Assets, Fair Value As Percentage of Par Value, Maximum	95.02%	[7]	93.79%	[8]	93.40%	[9]
Fair Value Inputs, Fair Value As Percentage of Par Value, Weighted Average	93.91%	[7]	92.22%	[8]	92.20%	[9]
Investment Grade Tax Exempt Securities Yield Spread Over Comparable Securities Minimum	352		437		467
Investment Grade Tax Exempt Securities Yield Spread Over Comparable Securities Maximum	467		484		525
Available-for-sale securities [Member] | Other debt securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Asset, Par Value	$ 4,400		$ 4,400		$ 4,400
Fair Value Inputs, Asset, Amortized Cost/Unpaid Principal Balance	4,400		4,400		4,400
Fair Value Inputs, Asset, Fair Value	$ 4,153		$ 4,151		$ 4,152
Fair Value Measurements, Valuation Techniques	Discounted cash flows	[1]	Discounted cash flows	[2]	Discounted cash flows	[3]
Fair Value Measurements, Significant Unobservable Input	Interest rate spread		Interest rate spread		Interest rate spread
Fair Value Inputs, Assets, Discount Rate, Minimum	6.65%	[10]	5.98%	[11]	6.01%	[12]
Fair Value Inputs, Assets, Discount Rate, Maximum	6.73%	[10]	6.03%	[11]	6.26%	[12]
Fair Value Inputs, Assets, Discount Rate, Weighted Average	6.72%	[10]	6.02%	[11]	6.23%	[12]
Fair Value Inputs, Assets, Fair Value As Percentage of Par Value, Minimum	94.38%	[7]	94.34%	[8]	94.34%	[9]
Fair Value Inputs, Assets, Fair Value As Percentage of Par Value, Maximum	94.38%	[7]	94.34%	[8]	94.36%	[9]
Fair Value Inputs, Fair Value As Percentage of Par Value, Weighted Average	94.38%	[7]	94.34%	[8]	94.36%	[9]
Average Yields On Comparable Short-term Taxable Securities, Maximum	3.00%		1.00%		1.00%
Residential mortgage loans held for sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Asset, Amortized Cost/Unpaid Principal Balance	$ 12,612		$ 9,957		$ 12,431
Fair Value Inputs, Asset, Fair Value	$ 12,100		$ 9,301		$ 11,617
Fair Value Measurements, Valuation Techniques	Quoted prices of loans sold in securitization transactions, with a liquidity discount applied		Quoted prices of loans sold in securitization transactions, with a liquidity discount applied		Quoted prices of loans sold in securitization transactions, with a liquidity discount applied
Fair Value Measurements, Significant Unobservable Input	Liquidity discount applied to the market value of a mortgage loans qualifying for sale to U.S. government agencies.		Liquidity discount applied to the market value of a mortgage loans qualifying for sale to U.S. government agencies.		Liquidity discount applied to the market value of a mortgage loans qualifying for sale to U.S. government agencies.
Liquidity Discount on Mortgage Loans Qualifying for Sale to US Govt Agencies	95.94%		93.41%		93.45%

[1] Discounted cash flows developed using discount rates primarily based on reference to interest rate spreads for comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies, adjusted for lack of trading volume

[2] Discounted cash flows developed using discount rates primarily based on reference to interest rate spreads for comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies, adjusted for lack of trading volume

[3] Discounted cash flows developed using discount rates primarily based on reference to interest rate spreads for comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies, adjusted for lack of trading volume

[4] Interest rate yields used to value investment grade tax-exempt securities represent a spread of 352 to 467 basis points over average yields for comparable tax-exempt securities.

[5] Interest rate yields used to value investment grade tax-exempt securities represent a spread of 437 to 484 basis points over average yields for comparable tax-exempt securities.

[6] Interest rate yields used to value investment grade tax-exempt securities represent a spread of 467 to 525 basis points over average yields for comparable tax-exempt securities.

[7] Represents fair value as a percentage of par value.

[8] Represents fair value as a percentage of par value.

[9] Represents fair value as a percentage of par value.

[10] Interest rate yields used to value investment grade taxable securities based on comparable short-term taxable securities which are generally yielding less than 3 percent.

[11] Interest rate yields used to value investment grade taxable securities based on comparable short-term taxable securities which are generally yielding less than 1 percent.

[12] Interest rate yields used to value investment grade taxable securities based on comparable short-term taxable securities which are generally yielding less than 1 percent.