Debt - 3.75% Convertible Senior Notes - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended			0 Months Ended	1 Months Ended			6 Months Ended	3 Months Ended
	Jun. 30, 2014	Sep. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 01, 2014	Dec. 31, 2014	Apr. 30, 2014	Jul. 31, 2013	Jun. 30, 2014	Mar. 31, 2015
Debt Instrument [Line Items]
Cash interest expense relating to interest coupon on convertible notes			$ 7,300,000	$ 12,400,000	$ 13,500,000
Non-cash interest expense related to the amortization of the debt			8,735,000	13,817,000	13,793,000
Loss on extinguishment on debt	2,100,000	4,200,000	2,148,000	4,181,000
Total consideration for repurchase of warrants			177,423,000
3.75% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Convertible notes, outstanding amount			360,000,000				360,000,000
Maturity date for notes			Oct. 01, 2014
Conversion rate per $ 1,000 principal of convertible notes			47.9789
Conversion price per share			$ 20.84				$ 20.84
Common Stock principal amount of convertible notes			1,000			1,000	1,000
Debt discount and increase in paid in capital			68,000,000				68,000,000
Interest rate of Senior Notes			3.75%				3.75%
Effective interest rate of convertible notes			8.43%				8.43%
Cancellation of convertible notes								56,300,000	54,700,000
Aggregate consideration for cancellation of convertible notes								120,200,000	98,600,000
Common shares surrendered by counter party									0.2
Value of convertible notes converted by a holder									1,200,000	15,300,000
Loss on extinguishment on debt			2,100,000	4,200,000
Reduction in stockholder's equity due to repurchase and conversion transactions			52,000,000	37,700,000
Consideration received from counter parties								9,200,000
Conversion settlement amount of convertible notes						1,000
Conversion of shares, stock issued						6.3
Warrants repurchased			7.2				0.1
Total consideration for repurchase of warrants			173,400,000				4,100,000
Gain (loss) on change in the fair value of the derivative liability			(11,600,000)
3.75% Convertible Senior Notes [Member] | Forecast [Member]
Debt Instrument [Line Items]
Warrants repurchased											4.7
3.75% Convertible Senior Notes [Member] | Additional Paid-in Capital [Member]
Debt Instrument [Line Items]
Reduction in stockholder's equity due to repurchase and conversion transactions			159,000,000
3.75% Convertible Senior Notes [Member] | Additional Warrant [Member]
Debt Instrument [Line Items]
Reduction in stockholder's equity due to repurchase and conversion transactions			145,400,000
Gain (loss) on change in the fair value of the derivative liability			$ 7,100,000
3.75% Convertible Senior Notes [Member] | Additional Warrant [Member] | Forecast [Member]
Debt Instrument [Line Items]
Warrants repurchased											4.7