Income Taxes - Summary of Differences Between Total Income Tax Expense Statutory Federal Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Expense Benefit [Line Items]
Other	$ (8,409)	$ 2,625	$ 10,204
Total expense	$ 459	$ 17	$ 0
TRS [Member]
Income Tax Expense Benefit [Line Items]
Statutory Rate	34.00%	34.00%	34.00%
Statutory rate applied to pre-tax income	$ 3,801	$ 3,384	$ (492)
State tax expense net of federal income tax	254	498	(72)
State deferred tax expense net of federal income tax	724	0	0
Permanent items	(241)	0	0
Deferred tax impact of federal rate change	19,391	0	0
Valuation allowance decrease based on impact of federal rate change	(23,470)	(4,039)	(1,169)
Other	0	174	1,733
Total expense	$ 459	$ 17	$ 0
Effective tax rate	4.11%	0.17%	0.00%