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Reconciliation of Beginning and Ending Liability Balances for Restructuring Charges (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Restructuring Cost And Reserve [Line Items]    
Accrual - Beginning balance $ 1,376 $ 3,028
Costs incurred and charged to expense   2,035
Costs paid or settled (1,014) (3,687)
Accrual - Ending balance 362 1,376
Twenty Sixteen Restructuring Plan    
Restructuring Cost And Reserve [Line Items]    
Accrual - Beginning balance 209  
Costs incurred and charged to expense   1,475
Costs paid or settled (209) (1,266)
Accrual - Ending balance   209
Twenty Fifteen Restructuring Plan    
Restructuring Cost And Reserve [Line Items]    
Accrual - Beginning balance 1,167 3,028
Costs incurred and charged to expense   560
Costs paid or settled (805) (2,421)
Accrual - Ending balance $ 362 $ 1,167