Convertible Senior Notes Due 2017 - Additional Information (Detail)	2 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) $ / shares	Sep. 30, 2015 USD ($) shares	Jun. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares	Jun. 30, 2014 USD ($)	Mar. 31, 2015 USD ($)
Debt Instrument [Line Items]
Conversion price, per share of common stock | $ / shares	$ 51.24		$ 51.24	$ 51.24
Principal settlement amount				$ 90,994,000	$ 1,000
Non-cash loss on extinguishment of Convertible Notes			$ (7,868,000)	(7,871,000)
Convertible Notes, aggregate principal amount	$ 167,800,000		167,800,000	$ 167,800,000
Scenario, Forecast [Member]
Debt Instrument [Line Items]
Principal settlement amount		$ 167,800,000
Common stock, shares issued on redemption of convertible notes | shares		1,769,609
Convertible Notes, aggregate principal amount		$ 167,800,000
Convertible Senior Notes Due 2017 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Convertible Notes, payment terms				The Company was required to pay interest semi-annually in arrears on April 1 and October 1 of each year.
Convertible Notes, aggregate principal amount	$ 258,800,000		$ 258,800,000	$ 258,800,000
Conversion rate of common stock, shares per principal amount				19.5172
Debt instrument convertible increment of principal amount of conversion				$ 1,000
Conversion price, per share of common stock | $ / shares	$ 51.24		$ 51.24	$ 51.24
Aggregate principal amount of convertible notes surrendered for conversion	$ 90,300,000		$ 90,300,000	$ 90,300,000		$ 700,000
Principal settlement amount	$ 90,300,000		$ 1,900,000
Common stock, shares issued on redemption of convertible notes | shares			1,049,679
Non-cash loss on extinguishment of Convertible Notes			$ 7,900,000	7,900,000
Forfeited accrued interest payable reclassified to additional paid-in capital				$ 300,000
Convertible Senior Notes Due 2017 [Member] | Senior Notes [Member] | Scenario, Forecast [Member]
Debt Instrument [Line Items]
Principal settlement amount		$ 167,800,000
Common stock, shares issued on redemption of convertible notes | shares		1,769,609
Non-cash loss on extinguishment of Convertible Notes		$ 13,000,000
Convertible Notes, aggregate principal amount		$ 167,800,000