Quarterly report pursuant to Section 13 or 15(d)

Debt Obligations - Information on Borrowings under Current and Prior Credit Facility and Applicable Interest Rates (Detail)

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Debt Obligations - Information on Borrowings under Current and Prior Credit Facility and Applicable Interest Rates (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Debt Disclosure [Abstract]        
Maximum amount outstanding under the credit facility during the period $ 1,053,598 $ 601,062 $ 1,053,598 $ 601,062
Average daily amount outstanding under the credit facility $ 922,719 $ 518,779 $ 804,490 $ 464,432
Weighted-average interest rate 3.62% 2.49% 3.50% 2.54%