Long-Term Debt - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	6 Months Ended					6 Months Ended						6 Months Ended				6 Months Ended		1 Months Ended
	Mar. 15, 2010	Mar. 31, 2010	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Common Class A [Member]	Jun. 30, 2013 Purchased call options [Member]	Dec. 31, 2012 Purchased call options [Member]	Jun. 30, 2013 Loans Payable [Member]	Jun. 29, 2011 Loans Payable [Member]	Jun. 30, 2013 Loans Payable [Member] LIBOR [Member] Minimum [Member]	Jun. 30, 2013 Loans Payable [Member] LIBOR [Member] Maximum [Member]	Jun. 30, 2013 Loans Payable [Member] Base Rate [Member] Minimum [Member]	Jun. 30, 2013 Loans Payable [Member] Base Rate [Member] Maximum [Member]	Jun. 30, 2013 Line of Credit [Member]	Jun. 29, 2011 Line of Credit [Member]	Jun. 30, 2013 Borrowing Base A Loan [Member]	Jun. 30, 2013 Borrowing Base B Loan [Member]	Jun. 30, 2013 Revolving Credit Facilities [Member]	Jun. 30, 2013 Convertible Senior Subordinated Notes [Member]	Jul. 31, 2013 Subsequent Event [Member]
Line of Credit Facility [Line Items]
Initiation date of term loan credit agreement								Jun. 29, 2011						Jun. 29, 2011
Term Credit Agreement			$ 0	$ 100,000,000					$ 100,000,000.0						$ 200,000,000.0
Borrowings term period									3 years						1 year
Interest rate base								LIBOR
Interest rate of credit agreement										2.50%	3.00%	1.50%	2.00%
Margin rate on borrowings																1.50%	2.00%
Revolving credit agreement borrowings																		200,000,000
Commitment fee percentage of average daily amount unused portion of revolving credit agreement			0.25%
Issuance costs of notes														2,200,000					8,500,000
Issue of cash convertible senior subordinated notes		375,000,000	375,000,000
Cash convertible senior subordinated notes due date		Mar. 15, 2015
Shareholder dilution up to a price per share		$ 31.50
Notes bear interest rate per year			3.50%
Date of commencing of notes			Sep. 15, 2010
Date of mature of notes			Mar. 15, 2015
Recognized original issue discount			73,800,000
Effective annual interest rate of notes			7.90%
Debt amount			1,000
Notes convertible based on initial conversion rate of shares			47.9185
Initial conversion price per share			$ 20.87
Initial conversion premium over closing sale			32.50%
Closing sale price of common stock on NASDAQ			$ 15.75
Percentage of price equal to principal amount of notes			100.00%
Deposit cash made to credit facilty to repurchase convertible notes																				375,000,000
Amount paid to enter into privately negotiated cash convertible note hedge transactions			73,700,000
Number of shares subject to adjustment of common stock			18,000,000
Common stock strike price					20.87
Financial instruments sold, not yet purchased, at fair value			1,512,983,000	1,445,437,000		0	200,000
Proceeds from sale of warrant	15,000,000
Common stock subject to adjustments strike price per share	$ 24.10
Initial valuation of embedded conversion derivative			73,800,000
Fair value of the embedded conversion derivative			$ 0	$ 200,000