Long-Term Obligations - Additional Information (Detail) (USD $) Share data in Millions, unless otherwise specified	1 Months Ended	3 Months Ended	6 Months Ended										1 Months Ended	6 Months Ended		1 Months Ended			6 Months Ended
	Feb. 28, 2011	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2013 At any time prior to May 9, 2015	Jun. 30, 2013 At any time prior to May 9, 2015 Equity offering redemption feature	Jun. 30, 2013 At any time after May 9, 2015 and before May 9, 2016	Jun. 30, 2013 At any time after May 9, 2016 and before May 9, 2017	Jun. 30, 2013 At any time after May 9, 2017 and before maturity	May 31, 2012 First Three Years	May 31, 2012 There After	May 31, 2012 Senior Convertible Notes Due 2018	Jun. 30, 2013 Senior Convertible Notes Due 2018	May 09, 2012 Senior Convertible Notes Due 2018	May 31, 2012 Senior Notes Due 2019	Jun. 30, 2013 Senior Notes Due 2019	May 09, 2012 Senior Notes Due 2019	Jun. 30, 2013 Senior Notes Due 2019 Asset Sale Redemption Right
Debt Instrument [Line Items]
Issuance date			Feb. 28, 2011
Convertible Notes at par	$ 230,000,000
Notes, maturity date			May 09, 2019											Feb. 01, 2018
Cash proceeds from the sale of the notes	222,700,000															42,600,000
Convertible notes exchanged, outstanding principal amount													107,600,000
Convertible Notes, outstanding principal amount			1,000															107,900,000
Convertible notes exchanged, warrants issued to purchase common stock													4.0
Convertible notes exchanged, warrants exercise price															1.863
Debt conversion converted instrument, principal amount																		1,000
Number of shares of common stock issued upon conversion of Notes			86.6739													23.4
Interest rate at which Notes bear cash interest			4.75%								3.00%	12.00%
Date Notes will reach fully accreted principal amount			May 09, 2015
Notes redemption price						100.00%	106.00%	106.00%	103.00%	100.00%									101.00%
Notes to be redeemed as a percentage of aggregate principal							35.00%
Gain upon the extinguishment of debt		21,800,000		21,800,000										21,800,000
Convertible Notes, debt issuance costs														2,200,000
Decrease in additional-paid-in-capital due to extinguishment of debt			13,400,000
Aggregate principal amount of securities remains outstanding immediately after occurrence of each redemption																	65.00%
Redemption period from date of closing of each equity offering																	90 days
Notice of redemption, minimum																	30 days
Notice of redemption, maximum																	60 days
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
Maximum trading price					98.00%