Note 16 - Statutory Information Segregated Funds Held for Others (Details) $ in Millions	Sep. 30, 2018 USD ($)
Segregated Funds Held for Others [Abstract]
Amounts held in escrow	$ 6.1

The amount as of the balance sheet date of deposits from our customers held in escrow at third party financial institutions and that is excluded from assets and liabilities in the consolidated balance sheets.

No definition available.

Name:	rdn_SegregatedFundsHeldforOthers
Namespace Prefix:	rdn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant