Percentage of voting equity interests acquired at the acquisition date in the business combination.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of liabilities incurred by the acquirer as part of consideration transferred in a business combination.

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Aggregate dividends declared during the period for each share of common stock outstanding.

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Amount of financial support provided to a nonconsolidated legal entity that is required to comply with or operate in accordance with requirements that are similar to those included in Rule 2a-7 of the Investment Company Act of 1940 for registered money market funds.

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SUBSEQUENT EVENTS - (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions					1 Months Ended			3 Months Ended			6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 01, 2018	Feb. 22, 2018	Feb. 16, 2018	Mar. 01, 2017	Nov. 30, 2017	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Dividends declared per share of common stock (in dollars per share)				$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.16	$ 0.24	$ 0.32	$ 0.27	$ 0.18
Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends declared per share of common stock (in dollars per share)			$ 0.08
Subsequent Event [Member] \| FNIC [Member] \| Financial Support, Capital Contributions [Member]
Subsequent Event [Line Items]
Nonconsolidated Legal Entity, Financial Support Amount	$ 30.0
Subsequent Event [Member] \| Crosswinds [Member] \| MNIC [Member]
Subsequent Event [Line Items]
Consideration transferred		$ 12.3
Subsequent Event [Member] \| TransRe [Member] \| MNIC [Member]
Subsequent Event [Line Items]
Consideration transferred		4.4
Liabilities incurred and paid		$ 5.0
Monarch Delaware Holdings LLC [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Percentage of voting interests acquired		50.00%
Transatlantic Reinsurance Company [Member] \| Monarch Delaware Holdings LLC [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Percentage of voting interests acquired		15.20%
Common Class A [Member] \| Monarch Delaware Holdings LLC [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Percentage of voting interests acquired		42.40%