Taxation - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net unpaid loss reserve discount	$ 96,357	$ 111,584
Net unearned premiums	95,676	80,434
Compensation liabilities	96,280	94,013
Net operating loss	323,716	181,295
Investment adjustments	14,030	14,399
Pension	6,817	10,370
Bad debt reserve	12,418	7,425
Amortizable goodwill	967	5,396
Net unrealized depreciation on investments	5,915	5,051
Stock options	7,249	16,192
Depreciation	26,525	13,299
Net realized capital losses	89,568	98,756
Deferred intercompany capital losses	18,221	26,164
Untaxed Lloyd's result	0	3,769
Deferred acquisition costs	17,820	31,133
Currency translation adjustments	0	6,280
Capital loss carryforwards, tax effected	71,651	5,047
Other	34,708	19,930
Deferred tax asset, gross of valuation allowance	917,918	730,537
Valuation allowance	367,366	276,301
Deferred Tax Assets, net of valuation allowance	550,552	454,236
Deferred tax liabilities:
Net unrealized appreciation on investments	21,500	51,010
Unremitted earnings	0	3,739
Deferred acquisition costs	10,858	8,308
Currency translation adjustments	12,813	1,210
Regulatory reserves	116,500	64,352
Deferred Tax Liabilities Unearned Revenue	4,380	0
Investment adjustment	5,269	6,373
Untaxed Lloyd's result	11,940	0
Depreciation expense	15,601	11,500
Syndicate capacity	82,106	92,756
Intangible assets	32,508	40,126
Other	3,806	13,202
Deferred tax liability	317,281	292,576
Net deferred tax assets	$ 233,271	$ 161,660