Segment Information - Long Lived Assets and Total Assets of Business Segments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Segment Reporting Information
Premiums and other receivables, net	$ 1,487,734	$ 1,541,760	$ 1,428,948
Deferred acquisition costs	275,931		263,523
Reinsurance recoverable, net	1,292,636	$ 1,401,681	1,394,308
Prepaid reinsurance premiums	518,082		575,747
Goodwill and Intangible assets, net	530,149		545,151
Prepaid and other assets	74,165		94,642
Corporate and other assets	5,839,146		5,454,215
Total assets	10,017,843		9,756,534
Property and Casualty
Segment Reporting Information
Premiums and other receivables, net	1,312,117		1,292,813
Deferred acquisition costs	249,825		239,293
Reinsurance recoverable, net	1,270,703		1,377,284
Prepaid reinsurance premiums	517,918		575,712
Goodwill and Intangible assets, net	424,339		436,724
Prepaid and other assets	49,910		56,960
Corporate and other assets	0		0
Total assets	3,824,812		3,978,786
Accident and Health
Segment Reporting Information
Premiums and other receivables, net	173,084		131,877
Deferred acquisition costs	26,106		24,230
Reinsurance recoverable, net	21,933		17,024
Prepaid reinsurance premiums	164		35
Goodwill and Intangible assets, net	105,810		108,427
Prepaid and other assets	19,191		32,852
Corporate and other assets	0		0
Total assets	346,288		314,445
Corporate and Other
Segment Reporting Information
Premiums and other receivables, net	2,533		4,258
Deferred acquisition costs	0		0
Reinsurance recoverable, net	0		0
Prepaid reinsurance premiums	0		0
Goodwill and Intangible assets, net	0		0
Prepaid and other assets	5,064		4,830
Corporate and other assets	5,839,146		5,454,215
Total assets	$ 5,846,743		$ 5,463,303