Variable Interest Entity - Summary of Information about Variable Interests (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Carrying Amount - Assets
Preferred stock	$ 25,000,000	$ 25,000,000
Note receivable - unsecured	28,121,000	18,748,000
Option	3,278,000	3,278,000
Total carrying amount - Assets	56,399,000	47,026,000
Maximum exposure to loss	$ 56,399,000	$ 55,026,000