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Employee Benefit Plans - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Pension Plans, Defined Benefit | Sweden      
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]      
Defined contribution plan, company contribution $ 539 $ 519 $ 485
Minimum      
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]      
Defined contribution plan, eligible age of employees 21 years    
Defined Contribution 401 K Plan      
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]      
Defined contribution plan, company contribution $ 451 $ 184 $ 141