Earnings Per Share - Additional Information (Detail) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2013 Performance Shares	Jun. 30, 2013 Maximum	Jun. 30, 2013 1.50% Convertible Notes	Mar. 18, 2013 1.50% Convertible Notes	Dec. 31, 2012 1.50% Convertible Notes	Jun. 30, 2013 2.50% Convertible Notes	Dec. 31, 2012 2.50% Convertible Notes	May 23, 2011 2.50% Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares	0.1	0	0.1
Debt instrument, interest rate, stated percentage				1.50%	1.50%	1.50%	2.50%	2.50%	2.50%