Investments Textuals (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Net Unrealized Gains Losses Recognized from Changes in Fair Value of Equity Securities Held	$ 367.6	$ (131.3)
Unrealized from changes in fair value of equity securities	355.6	(152.0)
Realized Investment Gains Losses From Impairment	$ 0.0	$ 0.0

The net realized gains or losses on impairments of investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

No definition available.

Name:	ori_RealizedInvestmentGainsLossesFromImpairment
Namespace Prefix:	ori_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration