Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic
Net income available to common shareholders	$ 16,926	$ 14,833	$ 32,642	$ 29,084
Less: Income attributable to unvested stock-based compensation awards	(266)	(228)	(527)	(458)
Net earnings allocated to common shareholders	$ 16,660	$ 14,605	$ 32,115	$ 28,626
Weighted average shares outstanding, including unvested stock-based compensation awards (in shares)	15,184,835	15,027,648	15,168,310	15,014,991
Less: unvested stock-based compensation awards (in shares)	(239,901)	(229,133)	(245,242)	(235,595)
Weighted average shares outstanding - Basic (in shares)	14,944,934	14,798,515	14,923,068	14,779,396
Diluted
Net earnings allocated to common shareholders	$ 16,660	$ 14,605	$ 32,115	$ 28,626
Weighted average shares outstanding - Basic (in shares)	14,944,934	14,798,515	14,923,068	14,779,396
Plus: Incremental shares from assumed conversion of stock-based compensation awards (in shares)	121,927	118,691	131,802	103,016
Weighted average shares outstanding - Diluted (in shares)	15,066,861	14,917,206	15,054,870	14,882,412
Basic EPS (in dollars per share)	$ 1.11	$ 0.99	$ 2.15	$ 1.94
Diluted EPS (in dollars per share)	$ 1.11	$ 0.98	$ 2.13	$ 1.92