Sale of Intellectual Property - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Jun. 30, 2017	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
Finite-Lived Intangible Assets [Line Items]
Revenue - other		$ 16,031	$ 4,469	$ 3,893	$ 3,465	$ 4,530	$ 2,043	$ 2,163	$ 3,009	$ 27,859	$ 11,745	$ 174,758
Revenue - other
Finite-Lived Intangible Assets [Line Items]
Revenue - other											2,303	$ 898
Intellectual property
Finite-Lived Intangible Assets [Line Items]
Proceeds from royalties	$ 600
Revenue - other											$ 600
Intellectual property | Revenue - other
Finite-Lived Intangible Assets [Line Items]
Revenue - other								$ 600