Commitments and Contingencies - Summary of Maximum Exposure under Guarantee (Detail) - SAC [Member] $ in Thousands	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Maximum guaranteed debt	$ 23,938
Equity investments	7,325	[1]
Maximum total exposure, including equity investments	$ 31,263

[1] Recorded in other assets on the Company’s consolidated balance sheets using the equity method.