Long-Term Obligations - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended	6 Months Ended
	May 09, 2012	Jun. 30, 2012	Jun. 30, 2012	May 31, 2012	Dec. 31, 2011
Debt Disclosure [Line Items]
Issuance date	Feb. 28, 2011
Convertible Notes at par				$ 230,000,000
Notes, maturity date	Feb. 01, 2018		May 09, 2019
Cash proceeds from the sale of the notes	222,700,000
Convertible Notes, outstanding principal amount		1,000	1,000
Debt conversion converted instrument, principal amount				1,000
Number of shares of common stock issued upon conversion of Notes			86.6739
Interest rate at which Notes bear cash interest		4.75%	4.75%
Date Notes will reach fully accreted principal amount			May 09, 2015
Gain upon the extinguishment of debt		21,800,000	21,800,000
Date of commencement of repayment of Notes			Aug. 01, 2011
Percentage of redemption price to principal amount of Notes			100.00%
Minimum number of trading days for first condition of convertibility of Notes			20
Number of trading days immediately preceding calendar quarter			30
Minimum percentage of conversion price on each applicable trading day			130.00%
Number of consecutive trading day period during five business day period			5
Debt conversion converted instrument, principal amount		1,000	1,000
Maximum trading price			98.00%
Notes, outstanding		293,382,000	293,382,000
Convertible notes, discount		78,328,000	78,328,000
Notes, carrying value		95,216,000	95,216,000		175,458,000
First Three Years
Debt Disclosure [Line Items]
Interest rate at which Notes bear cash interest				3.00%
There After
Debt Disclosure [Line Items]
Interest rate at which Notes bear cash interest				12.00%
At any time prior to May 9, 2015
Debt Disclosure [Line Items]
Notes redemption price		100.00%	100.00%
At any time prior to May 9, 2015 | Equity offering redemption feature
Debt Disclosure [Line Items]
Notes redemption price		106.00%	106.00%
Notes to be redeemed as a percentage of aggregate principal		35.00%	35.00%
At any time after May 9, 2015 and before May 9, 2016
Debt Disclosure [Line Items]
Notes redemption price		106.00%	106.00%
At any time after May 9, 2016 and before May 9, 2017
Debt Disclosure [Line Items]
Notes redemption price		103.00%	103.00%
At any time after May 9, 2017 and before maturity
Debt Disclosure [Line Items]
Notes redemption price		100.00%	100.00%
Senior Notes Due 2019
Debt Disclosure [Line Items]
Cash proceeds from the sale of the notes	46,800,000
Convertible Notes, outstanding principal amount				107,900,000
Number of shares of common stock issued upon conversion of Notes	23.4
Aggregate principal amount of securities remains outstanding immediately after occurrence of each redemption		65.00%	65.00%
Redemption period from date of closing of each equity offering		90 days	90 days
Notice of redemption		30 days	30 days
Notice of redemption		60 days	60 days
Senior Notes Due 2019 | Asset Sale Redemption Right
Debt Disclosure [Line Items]
Notes redemption price		101.00%	101.00%
Senior Convertible Notes Due 2018
Debt Disclosure [Line Items]
Convertible notes exchanged, outstanding principal amount	107,600,000
Convertible notes exchanged, warrants issued to purchase common stock	4,000,019
Convertible notes exchanged, warrants exercise price				1.863
Gain upon the extinguishment of debt			21,800,000
Convertible Notes, debt issuance costs		2,200,000	2,200,000
Notes, outstanding		122,400,000	122,400,000		230,000,000
Convertible notes, discount		27,200,000	27,200,000
Notes, carrying value		$ 95,216,000	$ 95,216,000		$ 175,458,000