Taxation - Reconciliation of effective tax rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected tax (benefit) provision	$ (2,527)	$ (31,080)	$ (50,797)
Permanent differences:
Non taxable (income) loss	(41,043)	(19,937)	(23,036)
Revision to prior year estimates	9,428	(24,121)	7,402
State, local and foreign taxes	37,455	23,157	27,499
Valuation allowance	2,510	1,197	9,517
Net allocated investment income	8,531	5,990	(405)
Stock awards	(3,132)	543	(433)
Non-deductible expenses	3,305	48,206	42,839
Other investment related adjustments	(1,753)	(905)	2,075
Adjustments related to Life Retro Arrangements	(9,815)	21,682	(35,045)
Change in tax rates	(8,105)	(6,233)	(11,877)
U.S. Tax Cuts and Jobs Act of 2017, net deferred tax asset revaluation	100,500
Uncertain tax positions	(36,284)	23,630	13,100
Total tax expense (benefit)	$ 59,070	$ 42,129	$ (19,161)