Earnings Per Share - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic
Net income available to common shareholders	$ 20,902	$ 17,394	$ 63,397	$ 50,037
Less: income attributable to unvested stock-based compensation awards	(318)	(266)	(1,024)	(792)
Net earnings allocated to common shareholders	$ 20,584	$ 17,128	$ 62,373	$ 49,245
Weighted average shares outstanding, including unvested stock-based compensation awards (in shares)	15,278,661	15,197,180	15,277,026	15,178,039
Less: unvested stock-based compensation awards (in shares)	(231,256)	(230,949)	(244,020)	(240,478)
Weighted average shares outstanding - Basic (in shares)	15,047,405	14,966,231	15,033,006	14,937,561
Diluted
Net earnings allocated to common shareholders	$ 20,584	$ 17,128	$ 62,373	$ 49,245
Weighted average shares outstanding - Basic (in shares)	15,047,405	14,966,231	15,033,006	14,937,561
Plus: Incremental shares from assumed conversion of stock-based compensation awards (in shares)	97,086	112,324	98,012	125,309
Weighted average shares outstanding - Diluted (in shares)	15,144,491	15,078,555	15,131,018	15,062,870
Basic EPS (in dollars per share)	$ 1.37	$ 1.14	$ 4.15	$ 3.30
Diluted EPS (in dollars per share)	$ 1.36	$ 1.14	$ 4.12	$ 3.27