Income taxes (Components of net deferred tax liability) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax asset
Tax losses carried forward	$ 116,416	$ 167,929
Deferred compensation	6,915	7,504
Deferred Tax Assets, Tax Deferred Expense, Other	2,039	2,047
Tax credits carried forward	5,469	2,761
Discounting of loss reserves	9,938	11,882
Unearned premiums reserve	6,647	4,291
Pension	5,943	5,503
Lloyd’s underwriting loss deductible in future periods	581	47
Other	4,943	4,111
Deferred tax asset, gross of valuation allowance	158,891	206,075
Valuation allowance	(98,065)	(167,929)
Net deferred tax asset	60,826	38,146
Deferred tax liability
Deferred acquisition costs	4,633	1,989
Intangibles	7,583	8,111
Unrealized appreciation on investments	3,179	7,073
Properties and fixed assets	2,593	2,044
Other	2,640	1,115
Deferred tax liability	20,628	20,332
Net deferred tax asset	$ 40,198	$ 17,814