Schedule II - Valuation and Qualifying Accounts and Reserves (Detail) - Allowance For Accounts Receivables [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year	$ 1,840	$ 2,006	$ 2,634
Additions	480	420	855
Deductions	226	586	1,483
Balance at end of year	$ 2,094	$ 1,840	$ 2,006