Percentage-of-completion method (Details 8) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Percentage-of-completion method [Line Items]
Costs and estimated earnings in excess of billings on uncompleted contracts	$ 65.0	$ 54.3
Billings in excess of costs and estimated earnings on uncompleted contracts	83.2	79.1
Amounts representing balances billed but not paid by customers under retainage provisions in contracts	56.3	51.5
Amounts of receivable retainage expected to be paid within one year or less	54.3	49.3
Long-term receivable retainage	$ 2.0	$ 2.2