Summary of Required Compliance Ratios in Connection with Terms of Credit Agreement (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Debt Instrument [Line Items]
Covenant, Tangible net worth	$ 125,000
Tangible net worth	$ 185,038
Total leverage	41.30%
Secured leverage	9.90%
Unencumbered leverage	37.40%
Fixed charge coverage	4.20%
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%