Insurance Activity - Summary of Losses and Loss Adjustment Reserve Activity (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2018		Dec. 31, 2017
Liability For Unpaid Claims And Claims Adjustment Expense Net [Abstract]
Balance at beginning of period	$ 474	[1]	$ 811
Incurred - prior periods	(73)		19
Paid or terminated - prior periods	(128)		(356)
Total losses and loss adjustment reserves	$ 273		$ 474	[1]

[1] Balances derived from audited financial statements as of December 31, 2017.