Acquisition of Platinum (Fair Value of Net Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Mar. 02, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Shareholders’ equity of Platinum prior to Special Dividend		$ 4,391,375	$ 4,866,577	$ 4,732,184
Platinum Underwriters Holdings, Ltd.
Adjustments for fair value, by applicable balance sheet caption:
Deferred acquisition costs	$ (44,486)
Debt	(28,899)
Reserve for claims and claim expenses	(21,725)
Other assets - deferred debt issuance costs	(1,046)
Total adjustments for fair value by applicable balance sheet caption before tax impact	(96,156)
Other assets - net deferred tax asset related to fair value adjustments	29,069
Total adjustments for fair value by applicable balance sheet caption	(67,087)
Adjustments for fair value of the identifiable intangible assets:
Identifiable indefinite lived intangible assets (insurance licenses)	8,400
Identifiable finite lived intangible assets (non-contractual relationships, renewal rights, value of business acquired, trade name, internally developed and used computer software and covenants not to compete)	75,200
Identifiable intangible assets before tax impact	83,600
Other liabilities - deferred tax liability on identifiable intangible assets	(13,115)
Total adjustments for fair value of the identifiable intangible assets	70,485
Total adjustments for fair value by applicable balance sheet caption and identifiable intangible assets	3,398
Shareholders’ equity of Platinum at fair value	1,487,473
Total net purchase price paid by RenaissanceRe	1,679,202
Excess purchase price over the fair value of net assets acquired assigned to goodwill	191,729
Platinum Underwriters Holdings, Ltd.
Business Acquisition [Line Items]
Shareholders’ equity of Platinum prior to Special Dividend	1,737,278
Cash and cash equivalents (Special Dividend on Platinum common shares and Platinum equity awards)	(253,203)
Adjusted shareholders’ equity of Platinum at March 2, 2015	$ 1,484,075