Debt Obligations - Information on Borrowings under Current and Prior Credit Facility and Applicable Interest Rates (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
Debt Disclosure [Abstract] | |||
Maximum amount outstanding under the credit facility during the period | $ 917,895 | $ 518,607 | $ 606,753 |
Average daily amount outstanding under the credit facility | $ 613,130 | $ 458,908 | $ 258,815 |
Weighted-average interest rate | 2.70% | 2.10% | 1.80% |