Other Non-Interest Expenses - Additional Information (Detail)	12 Months Ended
Dec. 31, 2016
Other Income And Expenses [Abstract]
Percentage of certain items exceeding interest and non interest income	1.00%
Percentage of expenses below threshold	1.00%

Percentage of certain items exceeding interest and non interest income.

No definition available.

Name:	rndb_PercentageOfCertainItemsExceedingInterestAndNonInterestIncome
Namespace Prefix:	rndb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration