Summary of Required Compliance Ratios in Connection with Terms of Credit Agreement (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Covenant, Tangible net worth	$ 125,000
Tangible net worth	$ 177,062	$ 181,203
Total leverage	41.90%	41.30%
Secured leverage	9.80%	9.80%
Unencumbered leverage	38.50%	37.60%
Fixed charge coverage	4.20%	4.30%
Maximum
Debt Instrument [Line Items]
Covenant, Total leverage	60.00%
Covenant, Secured leverage	30.00%
Covenant, Unencumbered leverage	60.00%
Minimum
Debt Instrument [Line Items]
Covenant, Fixed charge coverage	1.50%