Variable Interest Entities and Noncontrolling Interests - Variable interest entity (Details) - USD ($) $ in Thousands		1 Months Ended	6 Months Ended
	Jul. 02, 2019	Mar. 31, 2014	Jun. 30, 2020	Jun. 30, 2019
Variable Interest Entity [Line Items]
Net cash used for operating activities			$ 1,321,580	$ 712,524
Net cash used for investing activities			(1,810,190)	(746,944)
Net cash provided by financing activities			$ 671,337	(9,085)
Variable Interest Entity, Primary Beneficiary | Watford Holdings Ltd
Variable Interest Entity [Line Items]
Initial investment contribution amount		$ 100,000
Number of shares acquired		2,500,000
Ownership percentage		11.00%	13.00%
Senior notes, face amount	$ 175,000
Senior notes, stated percentage	6.50%
Proceeds from issuance of senior notes	$ 172,400
Senior notes acquired	$ 35,000
Net cash used for operating activities			$ 87,300	115,900
Net cash used for investing activities			78,000	(135,700)
Net cash provided by financing activities			$ (153,800)	$ 25,600