Common Stock and Earnings Per Share - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Mar. 11, 2015
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive potentially securities	32,500	35,400	40,200	35,400
Impact on diluted net income per share	$ 0.36	$ 0.60	$ 0.45	$ 0.99
Additional diluted outstanding shares	5,817,678	5,806,399	5,844,474	5,775,468
Convertible Note [Member]
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt instrument interest rate	4.50%		4.50%
Debt instrument interest rate terms			2020
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%
Impact on diluted net income per share			$ 0
Common stock exceeds conversion price			$ 68.90
Additional diluted outstanding shares	0		0