Goodwill and other intangible assets (Analysis of carrying value and accumulated amortization of intangible assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Goodwill And Other Intangible Assets [Line Items]
Finite-lived intangible assets, gross carrying amount	$ 60,343	$ 60,343
Finite-lived intangible assets, accumulated amortization	(43,253)	(37,587)
Indefinite-lived intangible assets, gross carrying amount	104,168	104,168
Trade name and customer relationships
Goodwill And Other Intangible Assets [Line Items]
Finite-lived intangible assets, gross carrying amount	18,189	18,189
Finite-lived intangible assets, accumulated amortization	(12,187)	(10,971)
Distribution network
Goodwill And Other Intangible Assets [Line Items]
Finite-lived intangible assets, gross carrying amount	39,831	39,831
Finite-lived intangible assets, accumulated amortization	(30,485)	(26,500)
Technology
Goodwill And Other Intangible Assets [Line Items]
Finite-lived intangible assets, gross carrying amount	2,323	2,323
Finite-lived intangible assets, accumulated amortization	(581)	(116)
Syndicate capacity
Goodwill And Other Intangible Assets [Line Items]
Indefinite-lived intangible assets, gross carrying amount	91,843	91,843
State licenses
Goodwill And Other Intangible Assets [Line Items]
Indefinite-lived intangible assets, gross carrying amount	$ 12,325	$ 12,325