Other intangible assets (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Carrying amount:
Balance at beginning of period	$ 22,169	$ 22,233
Foreign currency translation adjustment	(406)	(64)
Balance at end of period	21,763	22,169	22,233
Accumulated amortization:
Balance at beginning of period	2,704	2,226
Charge for the year	490	500	601
Foreign currency translation adjustment	(39)	(22)
Balance at end of period	3,155	2,704	2,226
Net book value:
Net book value	18,608	19,465	20,007
Trade Names
Carrying amount:
Balance at beginning of period	7,100	7,100
Foreign currency translation adjustment	0	0
Balance at end of period	7,100	7,100
Accumulated amortization:
Balance at beginning of period	0	0
Charge for the year	0	0
Foreign currency translation adjustment	0	0
Balance at end of period	0	0
Net book value:
Net book value	7,100	7,100	7,100
Favorable Lease Assets
Carrying amount:
Balance at beginning of period	13,460	13,503
Foreign currency translation adjustment	(489)	(43)
Balance at end of period	12,971	13,460
Accumulated amortization:
Balance at beginning of period	1,972	1,616
Charge for the year	354	368
Foreign currency translation adjustment	(78)	(12)
Balance at end of period	2,248	1,972
Net book value:
Net book value	10,723	11,488	11,887
Internet Sites
Carrying amount:
Balance at beginning of period	1,609	1,630
Foreign currency translation adjustment	83	(21)
Balance at end of period	1,692	1,609
Accumulated amortization:
Balance at beginning of period	732	610
Charge for the year	136	132
Foreign currency translation adjustment	39	(10)
Balance at end of period	907	732
Net book value:
Net book value	$ 785	$ 877	$ 1,020