Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Additional Information (Detail)

v2.4.0.8
Share-Based Compensation - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]        
Share-based compensation expense $ 0.6 $ 3.3 $ 1.8 $ 10.0
Unrecognized compensation cost related to nonvested common shares $ 5.5   $ 5.5  
Weighted average period for recognition of cost     3 years