Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reserve for Uncollectible Accounts:
Balance at Beginning of Period	$ 4,542	$ 3,114	$ 2,165
Additions	1,521	1,868	1,245
Deductions	(435)	(440)	(296)
Balance at End of Period	$ 5,628	$ 4,542	$ 3,114