Acquisition - Summary of Cash Consideration Paid, and Fair Values of Assets Acquired and Liabilities Assumed (Parenthetical) (Detail) $ in Millions	Jul. 03, 2016 USD ($)
Business Combinations [Abstract]
Book value of mortgage servicing rights	$ 789.3
Estimated fair value percentage of core deposit relationships	1.10%

Estimated fair value percentage of core deposit relationships.

No definition available.

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