Earnings Per Share - Additional Information (Detail) - shares	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Mar. 18, 2013	May. 23, 2011
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares	200,000	0
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt instrument, interest rate, stated percentage	1.50%	1.50%	1.50%	1.50%
Convertible Notes | 2.50% Senior Subordinated Notes Due June 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt instrument, interest rate, stated percentage	2.50%	2.50%	2.50%		2.50%
Performance Shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares	0	0