Debt Obligations - Information on Borrowings under Current and Prior Credit Facility and Applicable Interest Rates (Detail) - USD ($) |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2016 |
Jun. 30, 2015 |
Jun. 30, 2016 |
Jun. 30, 2015 |
|
| Line of Credit Facility [Abstract] | ||||
| Maximum amount outstanding during the period | $ 465,599,000 | $ 330,473,000 | $ 518,607,000 | $ 330,473,000 |
| Average daily amount outstanding under the credit facility | $ 426,172,000 | $ 171,638,000 | $ 449,101,000 | $ 132,213,000 |
| Weighted-average interest rate | 2.17% | 2.01% | 2.08% | 2.13% |