Segment Information - Summary of Company's Assets by Segment (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 12,850,350	$ 11,832,132
Operating Segments | Non-Life Run-Off
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	8,327,932	7,629,184
Operating Segments | Atrium
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	589,456	555,621
Operating Segments | StarStone
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	2,765,329	2,778,275
Operating Segments | Life and Annuities
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	1,694,773	1,734,945
Eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ (527,140)	$ (865,893)