Losses and Loss Adjustment Expenses - Reconciliation of Beginning and Ending Reserves for Losses and Loss Adjustment Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance as at January 1	$ 5,720,149
Other assets - Deferred Charge, Beginning balance	255,911
Net incurred losses and LAE:
Total net incurred losses and LAE	83,218	$ 70,136
Net paid losses:
Other assets - Deferred Charge, Ending balance	254,300
Balance as at March 31	6,641,507
Non-Life Run-of Segment, Atrium Segment, and Starstone Segment
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance as at January 1	5,720,149	4,509,421
Less: reinsurance reserves recoverable	1,360,382	1,154,196
Other assets - Deferred Charge, Beginning balance	255,911	0
Net balance as at January 1	4,103,856	3,355,225
Net incurred losses and LAE:
Current period	115,301	113,014
Prior periods	(32,083)	(42,878)
Total net incurred losses and LAE	83,218	70,136
Net paid losses:
Current period	(5,334)	(11,164)
Prior periods	(186,403)	(118,155)
Total net paid losses	(191,737)	(129,319)
Effect of exchange rate movement	4,881	(54,146)
Acquired on purchase of subsidiaries	0	774,758
Assumed business	1,084,251	189,868
Net balance as at March 31	5,084,469	4,206,522
Plus: reinsurance reserves recoverable	1,302,738	1,518,102
Other assets - Deferred Charge, Ending balance	254,300	0
Balance as at March 31	6,641,507	5,724,624
Non-Life Run-Off Segment
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance as at January 1	4,585,454	3,435,010
Less: reinsurance reserves recoverable	1,034,747	800,709
Other assets - Deferred Charge, Beginning balance	255,911	0
Net balance as at January 1	3,294,796	2,634,301
Net incurred losses and LAE:
Current period	6,069	20,726
Prior periods	(29,623)	(33,826)
Total net incurred losses and LAE	(23,554)	(13,100)
Net paid losses:
Current period	(1,990)	(4,571)
Prior periods	(130,323)	(60,689)
Total net paid losses	(132,313)	(65,260)
Effect of exchange rate movement	4,640	(38,238)
Acquired on purchase of subsidiaries	0	774,758
Assumed business	1,084,251	189,868
Net balance as at March 31	4,227,820	3,482,329
Plus: reinsurance reserves recoverable	977,096	1,210,933
Other assets - Deferred Charge, Ending balance	254,300	0
Balance as at March 31	5,459,216	4,693,262
Atrium
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance as at January 1	201,017	212,611
Less: reinsurance reserves recoverable	25,852	28,278
Net balance as at January 1	175,165	184,333
Net incurred losses and LAE:
Current period	16,062	14,878
Prior periods	(473)	(7,858)
Total net incurred losses and LAE	15,589	7,020
Net paid losses:
Current period	(2,238)	(2,870)
Prior periods	(5,510)	(9,041)
Total net paid losses	(7,748)	(11,911)
Effect of exchange rate movement	664	(3,198)
Net balance as at March 31	183,670	176,244
Plus: reinsurance reserves recoverable	26,249	26,629
Balance as at March 31	209,919	202,873
StarStone Segment
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance as at January 1	933,678	861,800
Less: reinsurance reserves recoverable	299,783	325,209
Net balance as at January 1	633,895	536,591
Net incurred losses and LAE:
Current period	93,170	77,410
Prior periods	(1,987)	(1,194)
Total net incurred losses and LAE	91,183	76,216
Net paid losses:
Current period	(1,106)	(3,723)
Prior periods	(50,570)	(48,425)
Total net paid losses	(51,676)	(52,148)
Effect of exchange rate movement	(423)	(12,711)
Net balance as at March 31	672,979	547,948
Plus: reinsurance reserves recoverable	299,393	280,540
Balance as at March 31	$ 972,372	$ 828,488