Income taxes (Components of net deferred tax asset) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax asset
Tax losses carried forward	$ 115,579	$ 116,416
Deferred compensation	4,924	6,915
Deferred interest expense	1,226	2,039
Tax credits carried forward	5,755	5,469
Discounting of loss reserves	5,137	9,938
Unearned premiums reserve	8,622	6,647
Pension	2,511	5,943
Lloyd’s underwriting loss deductible in future periods	0	581
Other	6,463	4,943
Total gross deferred income tax assets	150,217	158,891
Less: Valuation allowances	(86,272)	(98,065)
Total net deferred income tax assets	63,945	60,826
Deferred tax liability
Deferred acquisition costs	5,962	4,633
Intangibles	4,230	7,583
Unrealized appreciation on investments	1,477	3,179
Properties and fixed assets	2,387	2,593
Other	2,022	2,640
Total deferred income tax liabilities	16,078	20,628
Net deferred tax asset	$ 47,867	$ 40,198