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Segment Information - Geographic Information on Sales to External Customers (Detail) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Segment Reporting, Revenue Reconciling Item [Line Items]                      
Revenues $ 361,783 $ 331,096 $ 339,331 $ 325,894 $ 346,140 $ 296,129 $ 288,775 $ 265,765 $ 1,358,104 $ 1,196,809 $ 1,149,530
United States                      
Segment Reporting, Revenue Reconciling Item [Line Items]                      
Revenues                 734,033 622,276 580,724
Other                      
Segment Reporting, Revenue Reconciling Item [Line Items]                      
Revenues                 $ 624,071 $ 574,533 $ 568,806