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Summary of Receivables and Deferred Revenue from Contracts with Customers (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Balances from contracts with customers only:    
Accounts receivable $ 29,352 $ 27,585
Deferred revenue 1,547  
Revenue recognized in the period relating to:    
The beginning deferred revenue balance 434  
Changes in pricing related to products or services satisfied in previous periods 0  
Impairment losses on receivables $ 0