Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Basic
Net income available to common shareholders	$ 15,717	$ 14,251
Less: Income attributable to unvested stock-based compensation awards	(261)	(230)
Net earnings allocated to common shareholders	$ 15,456	$ 14,021
Weighted average shares outstanding, including unvested stock-based compensation awards (in shares)	15,151,521	15,002,332
Less: unvested stock-based compensation awards (in shares)	(250,583)	(242,056)
Weighted average shares outstanding - Basic (in shares)	14,900,938	14,760,276
Diluted
Net earnings allocated to common shareholders	$ 15,456	$ 14,021
Weighted average shares outstanding - Basic (in shares)	14,900,938	14,760,276
Plus: Incremental shares from assumed conversion of stock-based compensation (in shares)	141,676	87,340
Weighted average shares outstanding - Diluted (in shares)	15,042,614	14,847,616
Basic EPS (in dollars per share)	$ 1.04	$ 0.95
Diluted EPS (in dollars per share)	$ 1.03	$ 0.94