Fair Value Measurements - Additional Information (Detail) |
3 Months Ended | |||
|---|---|---|---|---|
|
Mar. 31, 2018
USD ($)
Contract
|
Mar. 31, 2018
GBP (£)
Contract
|
Dec. 31, 2017
USD ($)
Contract
|
Dec. 31, 2017
GBP (£)
Contract
|
|
| Forward Contract to Sell [Member] | ||||
| Derivative [Line Items] | ||||
| Number of forward contract outstanding | 1 | 1 | 1 | 1 |
| Forward contract outstanding | £ | £ 2,400,000 | £ 2,500,000 | ||
| Forward Contract to Purchase [Member] | ||||
| Derivative [Line Items] | ||||
| Number of forward contract outstanding | Contract | 1 | 1 | 1 | 1 |
| Forward contract outstanding | $ | $ 3,400,000 | $ 3,400,000 | ||
| Forward Contracts [Member] | ||||
| Derivative [Line Items] | ||||
| Forward contract terms | One 30-day forward contract | |||