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Derivative Instruments Schedule of Interest Rate Swaps by Maturity (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative, Fair Value, Net	$ 7,652	$ 6,929
Short [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	652,996	607,571
Derivative, Fair Value, Net	$ 11,461	$ 6,347
Weighted Average Pay Rate	2.15%	1.77%
Weighted Average Receive Rate	1.86%	1.40%
Derivative, Average Remaining Maturity	5 years 113 days	4 years 197 days
Short [Member] | Year 2018 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional		$ 65,990
Derivative, Fair Value, Net		$ 187
Weighted Average Pay Rate		0.97%
Weighted Average Receive Rate		1.38%
Derivative, Average Remaining Maturity		157 days
Short [Member] | Year 2019 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional		$ 19,540
Derivative, Fair Value, Net		$ 165
Weighted Average Pay Rate		1.41%
Weighted Average Receive Rate		1.60%
Derivative, Average Remaining Maturity		1 year 186 days
Short [Member] | Year 2020 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 86,000	$ 131,900
Derivative, Fair Value, Net	$ 1,372	$ 1,514
Weighted Average Pay Rate	1.60%	1.60%
Weighted Average Receive Rate	1.76%	1.41%
Derivative, Average Remaining Maturity	2 years 26 days	2 years 142 days
Short [Member] | Year 2021 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 161,400	$ 131,400
Derivative, Fair Value, Net	$ 2,428	$ 1,194
Weighted Average Pay Rate	2.03%	1.88%
Weighted Average Receive Rate	1.90%	1.40%
Derivative, Average Remaining Maturity	3 years 51 days	3 years 150 days
Short [Member] | Year 2022 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 68,480	$ 79,044
Derivative, Fair Value, Net	$ 1,511	$ 736
Weighted Average Pay Rate	2.00%	1.97%
Weighted Average Receive Rate	1.80%	1.39%
Derivative, Average Remaining Maturity	4 years 69 days	4 years 175 days
Short [Member] | Year 2023 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 150,466	$ 54,200
Derivative, Fair Value, Net	$ 1,984	$ 873
Weighted Average Pay Rate	2.38%	1.93%
Weighted Average Receive Rate	1.82%	1.37%
Derivative, Average Remaining Maturity	4 years 361 days	5 years 172 days
Short [Member] | Year 2024 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 8,900	$ 8,900
Derivative, Fair Value, Net	$ 316	$ 142
Weighted Average Pay Rate	1.99%	1.99%
Weighted Average Receive Rate	1.69%	1.34%
Derivative, Average Remaining Maturity	6 years 4 days	6 years 95 days
Short [Member] | Year 2025 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 57,822	$ 15,322
Derivative, Fair Value, Net	$ 361	$ 196
Weighted Average Pay Rate	2.62%	2.04%
Weighted Average Receive Rate	1.97%	1.37%
Derivative, Average Remaining Maturity	6 years 339 days	7 years 47 days
Short [Member] | Year 2026 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 40,885	$ 40,885
Derivative, Fair Value, Net	$ 3,423	$ 2,230
Weighted Average Pay Rate	1.63%	1.63%
Weighted Average Receive Rate	1.87%	1.36%
Derivative, Average Remaining Maturity	8 years 168 days	8 years 259 days
Short [Member] | Year 2027 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 30,000	$ 48,010
Derivative, Fair Value, Net	$ 934	$ 235
Weighted Average Pay Rate	2.29%	2.30%
Weighted Average Receive Rate	1.79%	1.40%
Derivative, Average Remaining Maturity	9 years 37 days	9 years 139 days
Short [Member] | Year 2028 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 36,663
Derivative, Fair Value, Net	$ (397)
Weighted Average Pay Rate	2.89%
Weighted Average Receive Rate	2.01%
Derivative, Average Remaining Maturity	9 years 339 days
Short [Member] | Year 2043 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 12,380	$ 12,380
Derivative, Fair Value, Net	$ (471)	$ (1,125)
Weighted Average Pay Rate	2.99%	2.99%
Weighted Average Receive Rate	1.83%	1.41%
Derivative, Average Remaining Maturity	25 years 47 days	25 years 139 days
Long [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 22,700	$ 9,700
Derivative, Fair Value, Net	$ 193	$ 563
Weighted Average Pay Rate	2.06%	1.36%
Weighted Average Receive Rate	2.80%	3.00%
Derivative, Average Remaining Maturity	4 years 307 days	7 years 197 days
Long [Member] | Year 2021 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 13,000
Derivative, Fair Value, Net	$ (1)
Weighted Average Pay Rate	2.31%
Weighted Average Receive Rate	2.66%
Derivative, Average Remaining Maturity	3 years 4 days
Long [Member] | Year 2025 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative notional	$ 9,700	$ 9,700
Derivative, Fair Value, Net	$ 194	$ 563
Weighted Average Pay Rate	1.72%	1.36%
Weighted Average Receive Rate	3.00%	3.00%
Derivative, Average Remaining Maturity	7 years 110 days	7 years 197 days

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Weighted average pay rate on interest rate swaps.

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13495-108611

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