Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

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Summary of Significant Accounting Policies - Additional Information (Detail)
$ in Thousands
12 Months Ended
Dec. 31, 2017
USD ($)
Entity
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Schedule Of Significant Accounting Policies [Line Items]      
Bed debt expense $ 3,200 $ 2,400 $ 2,000
Primary sources of revenue | Entity 3    
Revenue recognition access period (in years) 3 years    
Renewal of additional term license (in years) 1 year    
Advertising costs $ 22,800 19,400 $ 16,300
Cumulative effect of adoption of ASU 2016-09   43,843  
Deferred tax assets valuation allowance $ 517 0  
Leasehold improvements      
Schedule Of Significant Accounting Policies [Line Items]      
Property plant and equipment, useful life (in years) 12 years    
Software and Software Development Costs      
Schedule Of Significant Accounting Policies [Line Items]      
Property plant and equipment, useful life (in years) 5 years    
North America      
Schedule Of Significant Accounting Policies [Line Items]      
Net long-lived assets $ 140,000 125,300  
International Subsidiaries      
Schedule Of Significant Accounting Policies [Line Items]      
Net long-lived assets $ 8,400 $ 5,100  
Revenues      
Schedule Of Significant Accounting Policies [Line Items]      
Percentage of revenues 6.20% 5.70% 4.60%
Accounting Standards Update 2016-09, Excess Tax Benefit Component      
Schedule Of Significant Accounting Policies [Line Items]      
Deferred tax assets valuation allowance   $ 300  
Accumulated Deficit      
Schedule Of Significant Accounting Policies [Line Items]      
Cumulative effect of adoption of ASU 2016-09   43,837  
Accumulated Deficit | Accounting Standards Update 2016-09, Excess Tax Benefit Component      
Schedule Of Significant Accounting Policies [Line Items]      
Cumulative effect of adoption of ASU 2016-09   $ 43,800