Convertible Senior Notes - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended
	Dec. 31, 2012	Sep. 30, 2014	Dec. 12, 2012
Debt Instrument [Line Items]
Aggregate principal amount of Convertible Senior Notes		$ 189,750,000
Warrants [Member]
Debt Instrument [Line Items]
Warrants exercisable beginning	Mar. 01, 2018
Warrants exercisable ending	Oct. 18, 2018
Warrant expiration period	150 days
Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Aggregate principal amount of Convertible Senior Notes			189,800,000
Interest rate on Convertible Senior Notes			1.50%
Maturity date of Convertible Senior Notes		Dec. 01, 2017
Convertible notes conversion amount in multiples		1,000
Consecutive trading days		30 days
Common stock minimum trading days		20 days
Percentage of common stock conversion price		130.00%
Conditions for conversion of notes		During the five business day period after any five consecutive trading day period (the "measurement period") in which the trading price per $1,000 principal amount of the convertible notes for each trading day of the measurement period was less than 98% of the product of the last reported sales price of our common stock and the conversion rate on each trading day
Last day conversion rate		98.00%
Initial conversion rate per $1,000 principal amount		33.3042
Initial conversion price per share		$ 30.03
Percentage of repurchase price equal to principal amount of notes to be repurchased		100.00%
Redemption percentage of principal amount of notes outstanding by notice		25.00%
Redemption percentage of principal amount of notes outstanding at request by holders with accrued and unpaid interest		100.00%
Certain events of bankruptcy, insolvency or reorganization, redemption percentage of principal amount of notes outstanding with accrued and unpaid interest		100.00%
Notes Principal amount		1,000
Interest rate per annum		0.25%
Estimated fair value of the contingent interest feature of the notes		0
Convertible Senior Notes, term		5 years
Hedging of common stock	6,300,000
Cost of the Note Hedges		42,300,000
Aggregate proceeds from sale of warrants	$ 25,800,000
Purchase of common stock	6,300,000
Common stock, strike price per share	$ 40.04