Calculation of Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Calculation of Basic Earnings Per Share:
Net Income	$ 19,144	$ 20,367	$ 44,675
Weighted shares outstanding (shares)	16,317,224	15,286,842
Basic Earnings Per Share (in dollars per share)	$ 1.17	$ 1.33
Reconciliation of Numerator:
Net Income	$ 19,144	$ 20,367	$ 44,675
Reconciliation of Denominator:
Weighted shares outstanding - Basic (shares)	16,317,224	15,286,842
Effect of dilutive securities:
Share-based compensation (shares)	46,572	45,070
Adjusted denominator-Diluted (shares)	16,363,796	15,331,912
Diluted Earnings Per Share (in dollars per share)	$ 1.17	$ 1.33