Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts [Abstract]
Balance at beginning of period	$ 23,330	$ 21,993	$ 17,517
Charged to revenue and expenses	12,416	10,678	7,536
Charged to (from) other accounts	0	0	0
Deductions	(3,410)	(9,341)	(3,060)
Balance at end of period	$ 32,336	$ 23,330	$ 21,993