Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful receivables
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning of Period	$ 1,429	$ 1,251	$ 709
Charges to Costs and Expenses	541	941	855
Charges (Deductions) to Other Accounts	103	(123)	(53)
Deductions	(566)	(640)	(260)
End of Period	1,507	1,429	1,251
Tax valuation allowances
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning of Period	4,903	4,307	3,727
Charges to Costs and Expenses	886	762	1,615
Charges (Deductions) to Other Accounts	394	(140)	(272)
Deductions	(474)	(26)	(763)
End of Period	$ 5,709	$ 4,903	$ 4,307