Shareholders' Equity - Calculation of Numerator and Denominator in Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings per share
Net income (dollars in thousands)	$ 9,285	$ 8,952	$ 8,829	$ 8,895	$ 7,904	$ 7,071	$ 7,992	$ 6,710	$ 35,961	$ 29,677	$ 19,539
Weighted average shares outstanding									15,311,113	15,261,794	14,172,196
Basic earnings per share									$ 2.35	$ 1.94	$ 1.38
Diluted Earnings Per Share
Net income (dollars in thousands)	$ 9,285	$ 8,952	$ 8,829	$ 8,895	$ 7,904	$ 7,071	$ 7,992	$ 6,710	$ 35,961	$ 29,677	$ 19,539
Weighted average shares outstanding									15,311,113	15,261,794	14,172,196
Effect of dilutive stock options									125,998	170,326	185,586
Weighted average shares outstanding									15,437,111	15,432,120	14,357,782
Diluted earnings per share	$ 0.60	$ 0.58	$ 0.57	$ 0.58	$ 0.51	$ 0.46	$ 0.52	$ 0.44	$ 2.33	$ 1.92	$ 1.36