Multiemployer other postretirement and defined contribution plans (Details 15) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Multiemployer Plans, Postretirement Benefit [Member]
Multiemployer Plans [Line Items]
Multiemployer plan, period contributions	$ 37,100	$ 31,400	$ 24,000
Multiemployer Plans, Defined Contribution [Member]
Multiemployer Plans [Line Items]
Multiemployer plan, period contributions	$ 20,600	$ 18,700	$ 15,300