Performance Based Awards - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Unearned compensation expense	$ 4.3		$ 4.3
Performance Awards | Equity Incentive Plan 2013
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Performance awards, vesting period			2016-10
Performance awards, granted			1.4
Compensation expense	0.1
Performance Awards | Equity Incentive Plan 2012
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Performance awards, vesting period			2015-10
Performance awards, granted			0.7
Compensation expense	0.1	0.1
Performance awards, forfeitures			1.2
Performance Awards | Equity Incentive Plan 2012 and 2013
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Unearned compensation expense	$ 1.3		$ 1.3