Changes in accumulated other comprehensive income (loss) - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net (Gain) Loss, Net of Tax	$ 0.1	$ 0.2	$ 0.2	$ 0.3
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net (Gain) Loss, Tax	$ 0.1	$ (0.1)	$ (0.1)	$ (0.2)