Reconciliation of unrecognized tax benefits (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reconciliation of unrecognized tax benefits
Balance at the beginning of the year	$ 4,581	$ 4,755	$ 8,194
Additional uncertain tax provision identified during the year	2,720	403	0
Increase to uncertain tax provision on prior year positions	737	444	817
Uncertain tax provisions paid during the year	(737)	0	(642)
Decrease to uncertain tax provisions on prior year positions	(3,924)	0	(3,178)
Decreases as a result of expiration of the statute of limitations	(387)	(686)	0
Foreign exchange	(2)	(335)	(436)
Balance at the end of the year	2,988	4,581	4,755
Principal
Reconciliation of unrecognized tax benefits
Balance at the beginning of the year	2,874	3,169	4,550
Additional uncertain tax provision identified during the year	2,716	401	0
Increase to uncertain tax provision on prior year positions	559	151	600
Uncertain tax provisions paid during the year	(559)	0	(306)
Decrease to uncertain tax provisions on prior year positions	(2,302)	0	(1,500)
Decreases as a result of expiration of the statute of limitations	(351)	(622)	0
Foreign exchange	(2)	(225)	(175)
Balance at the end of the year	2,935	2,874	3,169
Interest
Reconciliation of unrecognized tax benefits
Balance at the beginning of the year	1,174	1,148	1,627
Additional uncertain tax provision identified during the year	(4)	2	0
Increase to uncertain tax provision on prior year positions	138	168	132
Uncertain tax provisions paid during the year	(138)	0	(192)
Decrease to uncertain tax provisions on prior year positions	(1,127)	0	(358)
Decreases as a result of expiration of the statute of limitations	(36)	(64)	0
Foreign exchange	0	(80)	(61)
Balance at the end of the year	7	1,174	1,148
Penalties
Reconciliation of unrecognized tax benefits
Balance at the beginning of the year	533	438	2,017
Additional uncertain tax provision identified during the year	8	0	0
Increase to uncertain tax provision on prior year positions	40	125	85
Uncertain tax provisions paid during the year	(40)	0	(144)
Decrease to uncertain tax provisions on prior year positions	(495)	0	(1,320)
Decreases as a result of expiration of the statute of limitations	0	0	0
Foreign exchange	0	(30)	(200)
Balance at the end of the year	$ 46	$ 533	$ 438