Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset	$ 349,140		$ 0
Operating Lease, Liability	348,186
Accounts receivable, allowance for doubtful accounts	$ 12,727		$ 15,345
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset		$ 343,000
Operating Lease, Liability		$ 340,000