Earnings Per Share - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Basic
Net income available to common shareholders	$ 21,040	$ 20,436
Less: income attributable to unvested stock-based compensation awards	(349)	(347)
Net earnings allocated to common shareholders	$ 20,691	$ 20,089
Weighted average shares outstanding, including unvested stock-based compensation awards (in shares)	15,313,635	15,271,930
Less: unvested stock-based compensation awards (in shares)	(253,460)	(258,452)
Weighted average shares outstanding - Basic (in shares)	15,060,175	15,013,478
Diluted
Net earnings allocated to common shareholders	$ 20,691	$ 20,089
Weighted average shares outstanding - Basic (in shares)	15,060,175	15,013,478
Plus: Incremental shares from assumed conversion of stock-based compensation awards (in shares)	76,348	99,040
Weighted average shares outstanding - Diluted (in shares)	15,136,523	15,112,518
Basic EPS (in dollars per share)	$ 1.37	$ 1.34
Diluted EPS (in dollars per share)	$ 1.37	$ 1.33