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Summary of Significant Accounting Policies - Accounting Pronouncements (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018
Net interest income	$ 28,176,000	$ 22,425,000	$ 78,579,000	$ 64,841,000
Net income	$ 9,642,000	$ 8,077,000	$ 25,392,000	$ 17,650,000
Diluted earnings per share (in dollars per share)	$ 0.32	$ 0.27	$ 0.84	$ 0.59
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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