Postretirement benefits (cash flows) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Postretirement benefits [Line Items]
Cash surrender value of insurance polices which fund pension plan	$ 6,914	$ 6,950
Postretirement benefit plan
Postretirement benefits [Line Items]
Company contributions	0	7,600
Expected benefit payments
2014	9,500
2015	9,600
2016	9,500
2017	9,800
2018	9,600
2019 - 2023	40,900
Pension plan
Expected benefit payments
2014	320
2015	310
2016	300
2017	290
2018	280
2019 - 2023	$ 1,240