Nature of Business and Summary of Significant Accounting Policies - Activity in Allowance for Doubtful Accounts Receivable (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts [Abstract]
Balance, beginning of period	$ (3,873)	$ (5,045)	$ (4,806)
Provision increase	(2,086)	(1,595)	(2,425)
Amounts written off, net of recoveries	1,305	2,551	2,088
Foreign currency translation adjustments and other	(145)	216	98
Balance, end of period	$ (4,799)	$ (3,873)	$ (5,045)