Reinsurance (Tables)

12 Months Ended

Dec. 31, 2017

Reinsurance Disclosures [Abstract]

Effect of reinsurance

The effect of reinsurance and retrocessional activity on premiums written and earned from property and casualty operations is shown below:

(U.S. dollars in thousands)	Premiums Written Year Ended December 31,									Premiums Earned Year Ended December 31,
	2017			2016			2015			2017			2016			2015
Direct	$	8,965,259		$	9,166,627		$	7,847,236		$	9,078,575		$	9,142,690		$	7,717,173
Assumed	5,787,313			4,458,981			2,821,771			4,903,909			4,074,817			3,465,421
Ceded	(4,084,148		)	(3,394,972		)	(2,780,183		)	(3,658,206		)	(3,451,620		)	(3,018,410		)
Net	$	10,668,424		$	10,230,636		$	7,888,824		$	10,324,278		$	9,765,887		$	8,164,184

Schedule of total reinsurance assets

The following table presents a summary of total reinsurance assets for the years ended December 31, 2017 and 2016:

(U.S. dollars in thousands)	2017		2016
Unpaid losses and loss expenses recoverable - P&C Operations	$	7,239,446	$	5,480,300
Unpaid losses and loss expenses recoverable - Corporate and Other	8,277		10,997
Total unpaid losses and loss expenses recoverable	7,247,723		5,491,297
Reinsurance balances receivable	930,114		577,479
Ceded unearned premiums	2,198,217		1,687,864
Total reinsurance assets	$	10,376,054	$	7,756,640

Allowance for uncollectible reinsurance

The following table presents a summary of the Company's allowance for uncollectible reinsurance at December 31, 2017 and 2016:

(U.S. dollars in thousands)	2017		2016
Allowance relating to unpaid losses and loss expenses recoverable	$	41,103	$	42,119
Allowance relating to reinsurance balances receivable	22,733		20,710
Total allowance for uncollectible reinsurance	$	63,836	$	62,829

Ratings profile of reinsurers

The following is an analysis of the total reinsurance assets, net of collateral held, at December 31, 2017, by reinsurers owing 3% or more of such total:

Name of Reinsurer	Reinsurer Financial Strength Rating	% of Total
Munich Reinsurance Co.	AA-/Stable	10.5	%
Lloyd's Syndicates	A+/Negative	7.4	%
Arch Reinsurance Company	A+/Negative	7.3	%
Transatlantic Reinsurance Company	A+/Stable	5.1	%
AXIS Reinsurance Co.	A+/Negative	5.0	%
Endurance Assurance Corporation	A/Positive	4.3	%
Hannover Rueck SE	AA-/Stable	3.5	%
National Indemnity Company	AA+/Negative	3.1	%
Swiss Reinsurance Co.	AA-/Stable	3.1	%
Everest Reinsurance (Bermuda) Ltd.	A+/Stable	3.0	%

The following table sets forth the ratings profile of the Company's reinsurers at December 31, 2017:

Reinsurer Financial Strength Rating	% of Total
AAA	—	%
AA	37.0	%
A	58.6	%
BBB	0.5	%
BB and below	0.7	%
Captives	3.1	%
Not Rated	0.1	%
Total	100.0	%