Earnings Per Share - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Mar. 18, 2013	May 23, 2011
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares	100,000	100,000
1.50% Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt instrument, interest rate, stated percentage	1.50%		1.50%	1.50%
2.50% Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt instrument, interest rate, stated percentage	2.50%		2.50%		2.50%
Performance Shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares	0	0