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, 2016	Mar. 31, 2015	Dec. 31, 2015
Calculation of Basic Earnings Per Share:
Net Income	$ 20,367	$ 21,109	$ 41,140
Weighted shares outstanding (shares)	15,286,842	14,604,841
Basic Earnings Per Share (in dollars per share)	$ 1.33	$ 1.45
Reconciliation of Numerator:
Net Income	$ 20,367	$ 21,109	$ 41,140
Reconciliation of Denominator:
Weighted shares outstanding - Basic (shares)	15,286,842	14,604,841
Effect of dilutive securities:
Share-based compensation (shares)	45,070	51,469
Adjusted denominator-Diluted (shares)	15,331,912	14,656,310
Diluted Earnings Per Share (in dollars per share)	$ 1.33	$ 1.44