Equity-Based Compensation - Summary of Equity-Based Compensation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation	$ 15,231	$ 11,859	$ 23,443
DSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation	430	341	234
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation	14,683	11,390	22,811
SARs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation	$ 118	$ 128	$ 398