Stockholder's Equity - Additional Information (Detail)	Sep. 30, 2018
Equity [Abstract]
Repurchase of shares to NAV per month, percentage	2.00%
Repurchase of shares to NAV per calender quarter, percentage	5.00%
Repurchase of shares outstanding less than one year to transaction price, percentage	95.00%

Percentage of repurchase price on transaction price.

No definition available.

Name:	oak_PercentageOfRepurchasePriceOnTransactionPrice
Namespace Prefix:	oak_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant