Common Stock and Earnings Per Share - Additional Information (Detail) - $ / shares		3 Months Ended		6 Months Ended
	Mar. 11, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Dilutive Securities Included And Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive potentially securities		81,250	25,000	87,500	40,200
Initial conversion price per share		$ 68.90		$ 68.90
Additional diluted outstanding shares		0	0	0	0
4.50% Convertible Senior Notes due 2020 [Member]
Dilutive Securities Included And Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Debt instrument interest rate	4.50%	4.50%		4.50%
Debt Instrument Maturity Year	2020			2020
Initial conversion price per share		$ 68.90		$ 68.90