Summary of Required Compliance Ratios in Connection with Terms of Credit Agreement (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Covenant, Tangible net worth	$ 125,000
Tangible net worth	$ 169,681	$ 181,203
Total leverage	42.00%	41.30%
Secured leverage	9.40%	9.80%
Unencumbered leverage	38.60%	37.60%
Fixed charge coverage	4.00%	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%