Earnings Per Common Share - Schedule of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Earnings from continuing operations	$ 13,321	$ 9,460	$ 14,551	$ 7,716	$ 9,335	$ 9,210	$ 13,529	$ 7,751	$ 45,048	$ 39,825	$ 39,478
Less dividend equivalents attributable to RSUs outstanding									(567)	(482)	(460)
Earnings from continuing operations attributable to common shareholders									44,481	39,343	39,018
Earnings (loss) from discontinued operations									2,138	(1,414)	(2,068)
Earnings (loss) from discontinued operations attributable to common shareholders									2,138	(1,414)	(2,068)
Net earnings attributable to common shareholders used for basic and diluted earnings per share calculation									$ 46,619	$ 37,929	$ 36,950
Weighted average common shares outstanding basic and diluted									36,897	33,806	33,420
RSUs outstanding at the end of the period	449				430				449	430	400
Basic and diluted earnings per common share									$ 1.26	$ 1.12	$ 1.11