Fair Value Qualitative information about Level 3 fair value measurements (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loans Receivable, Fair Value Disclosure	$ 5,206,753	$ 5,254,837
Impaired Loan Fair Value	3,867	3,574
Other Assets, Fair Value Disclosure	5,196,022	5,247,021
Loans Held-for-sale, Fair Value Disclosure	6,703	4,148
Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loans Receivable, Fair Value Disclosure	5,199,889	5,250,595
Impaired Loan Fair Value	3,867	3,574
Other Assets, Fair Value Disclosure	5,196,022	5,247,021
Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loans Receivable, Fair Value Disclosure	3,867	3,574
Other Assets, Fair Value Disclosure	6,152	6,520
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loans Receivable, Fair Value Disclosure	3,867	3,574
Other Assets, Fair Value Disclosure	6,152	6,520
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other Assets, Fair Value Disclosure	3,044	3,204
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other Assets, Fair Value Disclosure	$ 3,044	3,204
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Loans Receivable [Member] | Minimum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	11.10%
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Loans Receivable [Member] | Maximum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	15.20%
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Loans Receivable [Member] | Weighted Average [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	13.20%
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other Assets, Fair Value Disclosure	$ 3,044	$ 3,204
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Real Estate [Member] | Minimum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	0.00%	0.00%
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Real Estate [Member] | Minimum [Member] | Bulk Sale Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		15.00%
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Real Estate [Member] | Maximum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	90.00%	90.00%
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Real Estate [Member] | Maximum [Member] | Bulk Sale Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		15.00%
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Real Estate [Member] | Weighted Average [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	23.70%	24.50%
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Real Estate [Member] | Weighted Average [Member] | Bulk Sale Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		15.00%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loans Receivable, Fair Value Disclosure	$ 3,052	$ 2,735
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loans Receivable, Fair Value Disclosure	$ 3,052	2,735
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans Receivable [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired Loan Fair Value		$ 2,735
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans Receivable [Member] | Minimum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	0.00%	0.00%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans Receivable [Member] | Minimum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	9.00%	9.00%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans Receivable [Member] | Minimum [Member] | Cost Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Accumulated Depreciation	90.10%	90.10%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans Receivable [Member] | Maximum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	65.70%	90.00%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans Receivable [Member] | Maximum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	11.00%	11.00%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans Receivable [Member] | Maximum [Member] | Cost Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Accumulated Depreciation	90.10%	90.10%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans Receivable [Member] | Weighted Average [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	23.30%	22.70%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans Receivable [Member] | Weighted Average [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	9.90%	9.90%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans Receivable [Member] | Weighted Average [Member] | Cost Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Accumulated Depreciation	90.10%	90.10%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other Assets, Fair Value Disclosure	$ 2,295	$ 2,295
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Real Estate [Member] | Minimum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	0.90%	0.90%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Real Estate [Member] | Minimum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	13.00%	13.00%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Real Estate [Member] | Maximum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	68.40%	68.40%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Real Estate [Member] | Maximum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	13.00%	13.00%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Real Estate [Member] | Weighted Average [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	34.70%	34.70%
Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Real Estate [Member] | Weighted Average [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	13.00%	13.00%
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate - Remaining Commercial [Member] | Loans Receivable [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired Loan Fair Value		$ 127
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate - Remaining Commercial [Member] | Loans Receivable [Member] | Minimum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments		0.00%
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate - Remaining Commercial [Member] | Loans Receivable [Member] | Maximum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments		4.80%
Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate - Remaining Commercial [Member] | Loans Receivable [Member] | Weighted Average [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments		2.40%
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other Assets, Fair Value Disclosure	$ 813	$ 1,021
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other Assets, Fair Value Disclosure	$ 813	1,021
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Loans Receivable [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired Loan Fair Value		$ 712
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Loans Receivable [Member] | Minimum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	0.30%	0.30%
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Loans Receivable [Member] | Minimum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	10.50%	10.50%
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Loans Receivable [Member] | Maximum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	40.00%	33.00%
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Loans Receivable [Member] | Maximum [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	10.50%	10.50%
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Loans Receivable [Member] | Weighted Average [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	15.80%	12.50%
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Loans Receivable [Member] | Weighted Average [Member] | Income Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	10.50%	10.50%
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Other Assets, Fair Value Disclosure	$ 813	$ 1,021
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Real Estate [Member] | Minimum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	1.20%	1.20%
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Real Estate [Member] | Maximum [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	79.70%	79.70%
Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Real Estate [Member] | Weighted Average [Member] | Sales Comparison Approach Valuation Technique [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Comparability Adjustments	36.40%	31.80%
Construction Real Estate - Remaining Commercial [Member] | Fair Value, Measurements, Nonrecurring [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loans Receivable, Fair Value Disclosure	$ 119	$ 127
Construction Real Estate - Remaining Commercial [Member] | Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loans Receivable, Fair Value Disclosure	119	127
Fair Value [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired Loan Fair Value		$ 3,574
Fair Value [Member] | Fair Value, Measurements, Nonrecurring [Member] | Commercial Real Estate Portfolio Segment [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loans Receivable, Fair Value Disclosure	3,052
Fair Value [Member] | Fair Value, Measurements, Nonrecurring [Member] | Residential Real Estate [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loans Receivable, Fair Value Disclosure	696
Fair Value [Member] | Construction Real Estate - Remaining Commercial [Member] | Fair Value, Measurements, Nonrecurring [Member] | Construction Real Estate [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Loans Receivable, Fair Value Disclosure	$ 119