Significant transactions (Details) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020 USD ($) $ / shares	Sep. 30, 2020 USD ($) $ / shares	Aug. 06, 2020 contingent_value_right $ / shares shares
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Common shares par value (in dollars per share)	$ 0.01	$ 0.01
Payments for litigation | $		$ 2.2
TPRE shares
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Right to receive in cash (in dollars per share)			$ 0.905
Warrants issued (in shares) | shares			0.190
Value of warrants (in dollars per share)			$ 0.905
Merger agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Right to receive in cash (in dollars per share)			9.50
Other costs | $	$ 10.0	$ 10.0
Merger agreement | TPRE shares
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Common shares par value (in dollars per share)			$ 0.10
Right to receive common stock (in shares) | shares			0.743
Number of CVRs | contingent_value_right			1
Right to receive cash and equity (in dollars per share)			$ 13.73