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Summary of Significant Accounting Policies - Accounting Pronouncements (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018
Net interest income	$ 27,261,000	$ 21,800,000	$ 50,403,000	$ 42,416,000
Net income	$ 6,261,000	$ 5,146,000	$ 15,750,000	$ 9,573,000
Diluted earnings per share (in dollars per share)	$ 0.21	$ 0.17	$ 0.52	$ 0.32
Accounting Standards Update 2017-08 | Previously reported
Net interest income		$ 22,100,000		$ 42,900,000
Net income		$ 5,500,000		$ 10,000,000
Diluted earnings per share (in dollars per share)		$ 0.18		$ 0.33
Accounting Standards Update 2018-02 | Accumulated Other Comprehensive Income (Loss)
Cumulative effect of new accounting principle					$ 319,000
Accounting Standards Update 2018-02 | Retained Earnings
Cumulative effect of new accounting principle					$ (319,000)

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