Pensions - (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Amounts recognized in the consolidated balance sheets
Non-current assets	$ 0	$ 0
Current liabilities	0	0
Non-current liabilities	8,275	8,642
Amounts recognized in accumulated other comprehensive income (loss)
Net loss	(13,975)	(14,116)
Prior service cost	0	0
Net transitional obligation	0	0
Total amount recognized in other comprehensive loss	(13,975)	(14,116)
Information about pension plans
Projected benefit obligation	27,927	24,189	20,074	19,235
Accumulated benefit obligation	27,927	24,189
Fair value of plan assets	19,652	15,547	14,457	11,833
Components of net periodic pension benefit cost
Service cost
Interest cost on projected benefit obligation	1,154	1,062	1,088
Expected return on assets	(846)	(1,006)	(805)
Net amortization and deferrals	899	608	678
Net periodic benefit cost	1,207	664	961
Future benefit payments
2013	460
2014	517
2015	548
2016	577
2017	628
Next five years	3,643
Employers’ contributions	$ 2,719	$ 3,023	$ 2,552