Derivative instruments (Details)	12 Months Ended												1 Months Ended	12 Months Ended
	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2011 Cross-currency swap USD ($)	Dec. 31, 2010 Cross-currency swap USD ($)	Dec. 31, 2009 Cross-currency swap USD ($)	Dec. 31, 2010 Interest rate swap USD ($)	Dec. 31, 2009 Interest rate swap USD ($)	Sep. 30, 2010 Cash flow hedges Cross-currency swap Pay Euros EUR (€)	Sep. 30, 2010 Cash flow hedges Cross-currency swap Receive U.S. dollars USD ($)	Sep. 30, 2010 Terminated hedges Cross-currency swap USD ($)	Dec. 31, 2006 Terminated hedges Cross-currency swap USD ($)	Jun. 30, 2010 De-designated hedges Interest rate swap USD ($)	Dec. 31, 2010 De-designated hedges Interest rate swap USD ($)	Dec. 31, 2009 De-designated hedges Interest rate swap USD ($)	Jun. 30, 2008 De-designated hedges Interest rate swap USD ($)
Fair value of derivatives
Derivative liabilities					$ (262,000)										$ (6,100,000)
Derivative assets				1,011,000
Gain recognized in net income (loss)		1,254,000	1,852,000				1,254,000	1,852,000
Loss recorded in other comprehensive income (loss), net of taxes	(437,000)	(90,000)	(2,702,000)	(437,000)	(90,000)	(2,702,000)
Amortization term of instrument (in years)												10 years				3 years
Notional amount									33,500,000	45,500,000		63,000,000				150,000,000
Cash settlement amount											450,000
Fixed rate									5.00%	4.635%
Cash paid on settlement of derivative instrument													4,800,000
Gain on settlement of derivative instrument														1,300,000
Tax on unrealized loss on cross-currency swaps	$ 256,000	$ 36,000	$ 1,050,000	$ 256,000