Subsequent Event	12 Months Ended
Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Event	Subsequent EventOn December 30, 2020, the Company entered into an agreement with Cavello Bay Reinsurance Limited (Cavello), a subsidiary of Enstar Group Limited, under which Cavello will reinsure a legacy portfolio of excess workers’ compensation policies. The transaction closed on February 5, 2021. Under the terms of the transaction, based on reserves in place as of January 1, 2020, and adjusted for any subsequent claim activity, the Company ceded to Cavello approximately $690 million of net excess workers’ compensation liabilities relating to business written in 2007 and prior under a retroactive reinsurance agreement with an aggregate limit of $1 billion. The Company will recognize an after-tax loss of approximately $12 million in the first quarter of 2021.

The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-URI http://asc.fasb.org/topic&trid=2122774

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6842918&loc=SL6314017-165662

Name:	us-gaap_SubsequentEventsTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration