Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||||
|---|---|---|---|---|---|---|
Aug. 31, 2016 |
Apr. 01, 2016 |
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
|
| Goodwill and Intangible Assets Disclosure [Abstract] | ||||||
| Payment to acquire registrar credentials and related deferred tax liabilities | $ 0.2 | $ 1.5 | ||||
| Definite-lived intangible assets, weighted average amortization period | 6 years 1 month | |||||
| Amortization expense | $ 15.5 | $ 9.8 | $ 43.6 | $ 29.5 | ||