Share Based Compensation - Share Based Compensation Expense Included in Operating Expense (Income) (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]
Share-based and long-term incentive compensation	$ 7,201	$ 4,425	$ 4,474
General and Administrative Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based and long-term incentive compensation	6,177	3,323	2,451
Other Operating Expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based and long-term incentive compensation	$ 1,024	$ 1,102	$ 2,023