Debt - Schedule of Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Debt	$ 108,429	$ 110,358
Senior Notes
Line of Credit Facility [Line Items]
Debt	0	5,200
Convertible Debt
Line of Credit Facility [Line Items]
Debt	108,139	104,673
Other Indebtedness
Line of Credit Facility [Line Items]
Debt	$ 290	$ 485