Earnings Per Common Share - Computation of Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Earnings from continuing operations	$ 13,408	$ 11,017	$ 13,823	$ 10,162	$ 13,321	$ 9,460	$ 14,551	$ 7,716	$ 48,410	$ 45,048	$ 39,825
Less dividend equivalents attributable to RSUs outstanding									(751)	(567)	(482)
Earnings from continuing operations attributable to common stockholders									47,659	44,481	39,343
Earnings (loss) from discontinued operations									(704)	2,138	(1,414)
Earnings (loss) from discontinued operations attributable to common stockholders									(704)	2,138	(1,414)
Net earnings attributable to common stockholders used for basic and diluted earnings per share calculation									$ 46,955	$ 46,619	$ 37,929
Basic									40,171	36,897	33,806
Incremental shares from stock-based compensation									20
Diluted									40,191	36,897	33,806
Basic earnings per common share									$ 1.17	$ 1.26	$ 1.12
Diluted earnings per common share	$ 0.32	$ 0.27	$ 0.33	$ 0.25	$ 0.33	$ 0.24	$ 0.43	$ 0.28	$ 1.17	$ 1.26	$ 1.12