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Value of common stock held in trust.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Price of a single share of a number of saleable stocks of a company.

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Significant transactions - Easterly Acquisition Corp., WRM America Indemnity Company, Inc. and The Phoenix Holdings Ltd. (Details) $ / shares in Units, $ in Millions							12 Months Ended
	Nov. 16, 2018 USD ($)	Nov. 05, 2018 USD ($) $ / shares employee shares	Nov. 02, 2018 USD ($) $ / shares shares	Sep. 30, 2018 $ / shares	Aug. 22, 2018 shares	Aug. 16, 2018 USD ($)	Dec. 31, 2018 USD ($) shares
Significant transactions
Value of shares redeemed		$ 164.0
Shares issued \| shares							4,670,531
Share-based compensation expense							$ 2.5
Stock redeemed (in shares) \| shares							9,519,280
ESPP
Significant transactions
Minimum number of shares to be purchased \| shares					100
Maximum number of shares to be purchased \| shares					1,000
Preference Share Investors \| Private Placement \| Series B preference shares
Significant transactions
Share subscriptions (in shares) \| shares		11,901,670
The Phoenix
Significant transactions
Charge on termination of share repurchase agreement							$ 4.5
Merger Agreement
Significant transactions
Gross proceeds		$ 226.1
Proceeds from merger, private placement and employee stock purchase plan		$ 268.0
Merger Agreement \| Private Placement
Significant transactions
Number of Times of Diluted Book Value Per Share, Exchange Price of Share		1.05
Adjusted diluted book value per share \| $ / shares		17.22447
Merger Agreement \| ESPP
Significant transactions
Number of Times of Diluted Book Value Per Share, Exchange Price of Share		1.05
Minimum number of shares to be purchased \| shares		100
Maximum number of shares to be purchased \| shares		1,000
Loan repayment term		2 years
Number of employees that purchased shares \| employee		405
Number of common shares purchased \| shares		149,236
Share-based compensation expense		$ 2.6
Merger Agreement \| CM Bermuda
Significant transactions
Adjustment to consideration payable	$ 1.6
Merger related contractual costs	9.0
Merger related legal, advisory and other costs	$ 7.1
Merger Agreement \| CM Bermuda \| Common shares
Significant transactions
Reported book value per share (in dollars per share) \| $ / shares				$ 16.44
Subscription Agreement \| Preference Share Investors \| Private Placement
Significant transactions
Warrants Received \| shares		5,418,434
Exercisable period of warrants		5 years
Strike price as a percentage of the per share purchase price		125.00%
Warrant strike price per share \| $ / shares		$ 21.53
Cost value of warrants		$ 9.6
Stock issuance costs		$ 2.0
Subscription Agreement \| Preference Share Investors \| Private Placement \| Series B preference shares
Significant transactions
Share subscriptions (in shares) \| shares		11,901,670
Value of share subscriptions		$ 195.8
Subscription Agreement \| Preference Share Investors \| Private Placement \| Series B preference shares \| Common shares
Significant transactions
Share subscriptions (in shares) \| shares		1,225,954
Value of share subscriptions		$ 20.8
Redemption Agreement \| CM Bermuda \| Common shares
Significant transactions
Value of shares redeemed			$ 164.0
Stock redeemed (in shares) \| shares			9,519,280
Share price (in dollars per share) \| $ / shares			$ 17.22447
Redemption Agreement \| IMGAH
Significant transactions
Redemption amount of preference shares		$ 95.0
For the first 100 shares \| ESPP
Significant transactions
Purchase price of common shares as a percentage on its market value					85.00%
For the first 100 shares \| Merger Agreement \| ESPP
Significant transactions
Purchase price of common shares as a percentage on its market value		85.00%
For the next 900 shares \| ESPP
Significant transactions
Purchase price of common shares as a percentage on its market value					100.00%
For the next 900 shares \| Merger Agreement \| ESPP
Significant transactions
Purchase price of common shares as a percentage on its market value		100.00%
Easterly \| Merger Agreement
Significant transactions
Public shares held by Easterly's public stockholders in trust		$ 39.3	$ 149.0
Shares issued \| shares		2,280,241
Issuance of converted warrants \| shares		6,088,535
Easterly \| Merger Agreement \| Common shares
Significant transactions
Number of Times of Diluted Book Value Per Share, Exchange Price of Share				1.05
Exchange ratio		0.609
Value of shares redeemed		$ 109.7
WRM America Indemnity Company, Inc.
Significant transactions
Percentage of ownership interest acquired						100.00%
Consideration						$ 16.9
Acquisition of intangible assets						$ 3.1