Goodwill and Other Intangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Feb. 01, 2016	Mar. 31, 2017	Dec. 31, 2016
Schedule Of Acquired Intangible Assets By Major Class [Line Items]
Goodwill and other intangible assets			$ 2,208,612	$ 2,203,653
Brooklyn Underwriting Pty Limited and Brooklyn IT Pty Limited [Member]
Schedule Of Acquired Intangible Assets By Major Class [Line Items]
Finite-lived intangible assets acquired	$ 22,900
Allied International Holdings, Inc.
Schedule Of Acquired Intangible Assets By Major Class [Line Items]
Finite-lived intangible assets acquired		$ 6,000
Total identified intangible assets		14,000
Goodwill acquired during the period		$ 14,100