Revolving Credit Facility - Additional Information (Detail) - USD ($) |
Sep. 30, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Line of Credit Facility [Line Items] | ||
| Outstanding amount | $ 35,000,000 | $ 355,000,000 |
| Revolving credit facility [Member] | ||
| Line of Credit Facility [Line Items] | ||
| Remaining borrowing capacity | 433,300,000 | |
| Maximum borrowing capacity | 500,000,000 | |
| Outstanding amount | 35,000,000 | 355,000,000 |
| Letters of credit issued | $ 31,700,000 | $ 27,200,000 |