Calculation of Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Calculation of Basic Earnings Per Share:
Net Income	$ 6,046	$ 8,029	$ 25,190	$ 28,396	$ 44,675
Weighted shares outstanding (shares)	16,340,665	15,315,020	16,329,009	15,300,931
Basic Earnings Per Share (in dollars per share)	$ 0.37	$ 0.52	$ 1.54	$ 1.86
Reconciliation of Numerator:
Net Income	$ 6,046	$ 8,029	$ 25,190	$ 28,396	$ 44,675
Reconciliation of Denominator:
Weighted shares outstanding - Basic (shares)	16,340,665	15,315,020	16,329,009	15,300,931
Effect of dilutive securities:
Share-based compensation (shares)	41,542	37,682	44,029	41,356
Adjusted denominator-Diluted (shares)	16,382,207	15,352,702	16,373,038	15,342,287
Diluted Earnings Per Share (in dollars per share)	$ 0.37	$ 0.52	$ 1.54	$ 1.85