Basis of Presentation and Significant Accounting Policies - Accounts Receivable (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			$ 5,594	$ 5,356	$ 5,356
Provision for doubtful accounts	$ 5,700	$ 4,400	11,636	$ 8,409	19,405
Write-offs and adjustments			(10,593)		(19,167)
Balance at end of period	$ 6,637		$ 6,637		$ 5,594