Employee benefit Plans - Individually Significant Multiemployer Pension Plans (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2012
Multiemployer Plans [Line Items]
High end of funded percentage of multiemployer plans in critical status	65.00%
High end of funded percentage of multiemployer plans in endangered status	80.00%
Surcharge percentage during first twelve months on contribution rates for plans certified as endangered, seriously endangered or critical	5.00%
Period for which surcharge is 5% on contribution rates for plans certified as endangered, seriously endangered or critical	12 months
Surcharge percentage after first twelve months on contribution rates for plans certified as endangered, seriously endangered or critical	10.00%
Description of multiemployer defined benefit pension plan	A multiemployer defined benefit pension plan that has been certified as endangered, seriously endangered or critical may begin to levy a statutory surcharge on contribution rates. Once authorized, the surcharge is at the rate of 5% for the first 12 months and 10% for any periods thereafter. Contributing employers, however, may eliminate the surcharge by entering into a collective bargaining agreement that meets the requirements of the applicable FIP or RP.
Minimum percentage of total contributions relating to multiemployer plans endangered, seriously endangered or critical	5.00%