Segment Information - Summary of Company's Assets by Segment (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 12,659,166	$ 11,832,132
Operating Segments | Non-life Run-off
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	8,337,022	7,629,184
Operating Segments | Atrium
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	577,235	555,621
Operating Segments | StarStone
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	2,915,503	2,778,275
Operating Segments | Life and annuities
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	1,687,902	1,734,945
Eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ (858,496)	$ (865,893)