Computation of Earnings Per Share - Summary of Calculation of Basic Earnings Per Common Share and Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income	$ 30,281	$ 17,571	$ 51,406	$ 28,966
Denominator:
Denominator for basic earnings per share–weighted average common shares	25,766	25,501	25,732	25,477
Effect of dilutive stock options	167	100	170	108
Effect of other common stock equivalents	421	399	424	397
Denominator for diluted earnings per share–adjusted weighted average common shares	26,354	26,000	26,326	25,982
Basic Earnings Per Share	$ 1.18	$ 0.69	$ 2.00	$ 1.14
Diluted Earnings Per Share	$ 1.15	$ 0.68	$ 1.95	$ 1.12