Notes Payable, Collateralized and Short-Term Borrowings - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended				6 Months Ended		3 Months Ended		6 Months Ended			6 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended		3 Months Ended	6 Months Ended			3 Months Ended		6 Months Ended		12 Months Ended		6 Months Ended			12 Months Ended		6 Months Ended		6 Months Ended			1 Months Ended	3 Months Ended		6 Months Ended					6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Credit Agreement [Member]	Jun. 30, 2012 Credit Agreement [Member]	Jun. 30, 2013 Credit Agreement [Member]	Jun. 30, 2012 Credit Agreement [Member]	Dec. 31, 2012 Credit Agreement [Member]	Jun. 23, 2011 Credit Agreement [Member]	Jun. 30, 2013 Maximum [Member]	Jun. 30, 2013 Minimum [Member]	Jun. 30, 2013 Secured Loan Arrangements [Member]	Jun. 30, 2012 Secured Loan Arrangements [Member]	Jun. 30, 2013 Secured Loan Arrangements [Member]	Jun. 30, 2012 Secured Loan Arrangements [Member]	Dec. 31, 2012 Secured Loan Arrangements [Member]	Jun. 30, 2013 Capped call [Member]	Jul. 25, 2011 Capped call [Member]	Jun. 30, 2013 Sale Leaseback Transactions [Member]	Jun. 30, 2012 Sale Leaseback Transactions [Member]	Jun. 30, 2013 Sale Leaseback Transactions [Member]	Jun. 30, 2012 Sale Leaseback Transactions [Member]	Dec. 31, 2011 Sale Leaseback Transactions [Member]	Dec. 31, 2010 Sale Leaseback Transactions [Member]	Jun. 30, 2013 Lease Termination [Member]	Jun. 30, 2013 Computer Software [Member]	Jun. 30, 2013 Furniture and Fixtures [Member]	Jun. 30, 2013 Class A Common Stock [Member] Capped call [Member]	Jun. 30, 2013 8.75% Convertible Notes [Member]	Jun. 30, 2012 8.75% Convertible Notes [Member]	Jun. 30, 2013 8.75% Convertible Notes [Member]	Jun. 30, 2012 8.75% Convertible Notes [Member]	Dec. 31, 2012 8.75% Convertible Notes [Member]	Apr. 01, 2010 8.75% Convertible Notes [Member]	Jun. 30, 2013 8.75% Convertible Notes [Member] Class A Common Stock [Member]	Jun. 30, 2013 4.50% Convertible Notes [Member]	Jun. 30, 2012 4.50% Convertible Notes [Member]	Dec. 31, 2012 4.50% Convertible Notes [Member]	Jul. 29, 2011 4.50% Convertible Notes [Member]	Jun. 30, 2013 4.50% Convertible Notes [Member] Embedded conversion feature [Member]	Jun. 30, 2013 4.50% Convertible Notes [Member] Capped call [Member]	Jun. 30, 2013 4.50% Convertible Notes [Member] Class A Common Stock [Member]	Jul. 25, 2011 4.50% Convertible Notes [Member] Class A Common Stock [Member]	Jun. 30, 2013 4.50% Convertible Notes [Member] Class A Common Stock [Member] Capped call [Member]	Jun. 30, 2012 8.125% Senior Notes [Member]	Jun. 30, 2013 8.125% Senior Notes [Member]	Jun. 30, 2012 8.125% Senior Notes [Member]	Jun. 30, 2013 8.125% Senior Notes [Member]	Jun. 30, 2012 8.125% Senior Notes [Member]	Jun. 26, 2013 8.125% Senior Notes [Member]	Dec. 31, 2012 8.125% Senior Notes [Member]	Jun. 26, 2012 8.125% Senior Notes [Member]	Jun. 30, 2013 Condition One [Member]	Jun. 30, 2013 Condition Two [Member]
Debt Instrument [Line Items]
Convertible notes (rate)																					6.00%		6.00%								8.75%	8.75%	8.75%	8.75%	8.75%			7.61%		7.61%
Stated interest rate																															8.75%		8.75%		8.75%	8.75%		4.50%		4.50%	4.50%							8.125%		8.125%		8.125%	8.125%
Principal amount of notes																															$ 150,000,000		$ 150,000,000		$ 150,000,000	$ 150,000,000		$ 160,000,000		$ 160,000,000	$ 160,000,000													$ 112,500,000
Number of shares to be delivered upon conversion																														15,700,000			23,573,484		23,384,070		23,600,000	16,260,160		16,260,160				16,300,000
Interest expense recorded on senior notes	2,900,000	2,900,000																													3,300,000	3,300,000	6,600,000	6,600,000				5,800,000	5,800,000									2,300,000	100,000	4,600,000	100,000
Senior Notes maturity date																																	Apr. 15, 2015		Apr. 15, 2015			Jul. 15, 2016		Jul. 15, 2016
Conversion rate for convertible debt																																					157.1566							101.6260
Dividend reference amount																																					$ 0.10							$ 0.17
Principal amount of notes																																					1,000							1,000
Adjustments to paid-in capital																																										19,000,000
Adjustments to additional paid-in capital, net of taxes and issuance costs																			9,900,000																							16,100,000
Carrying amount of debt component	423,805,000		423,805,000		451,444,000																										150,000,000		150,000,000		150,000,000			145,595,000		143,354,000					137,200,000			108,842,000		108,842,000			108,780,000	108,700,000
Debt issuance costs																																						3,800,000									200,000			3,800,000
Cap price																				12.30																							12.72
Strike price of capped call transaction																																														$ 10.17
Percent over sale price of stock																																														50.00%
Redemption price as percentage of principal amount			100.00%
Earliest call date																																																		Jun. 26, 2017
Secured loan arrangements fixed rate, minimum																2.62%
Secured loan arrangements fixed rate, maximum																8.09%
Outstanding balance of the secured loan arrangements														19,400,000		19,400,000		37,600,000
Value of the fixed assets pledged	16,900,000		16,900,000		32,100,000
Interest expense	9,989,000	7,578,000	19,689,000	15,136,000		100,000	700,000	200,000	800,000					600,000	300,000	900,000	700,000				400,000	300,000	600,000	600,000
Final payment due, for secured loan arrangement																2016-12
Prepayment of secured loan	12,200,000		12,200,000
Early termination fees	100,000		100,000																								100,000
Acceleration of deferred financing costs	100,000		100,000																								200,000
Furniture, equipment and software sold																									34,200,000	34,200,000
Term of secured financing arrangement																												36 months	48 months
Maturity date																							2014-09
Prepayment of outstanding lease balance																											7,400,000
Outstanding balance of the leases	0		0		11,700,000
Value of the fixed assets pledged	0		0		8,300,000
Unsecured revolving credit											130,000,000
Applicable margin												3.00%	2.00%																																										0.50%	1.00%
Maximum applicable margin												4.00%	3.00%
Minimum outstanding loan balance			0
Maximum period outstanding			270 days
Days outstanding loan balance reduced to zero			3 days
Interest rate for credit agreement			Credit Agreement will bear interest at a per annum rate equal to, at the Company's option, either (a) a base rate equal to the greatest of (i) the prime rate as established by the Administrative Agent from time to time, (ii) the average federal funds rate plus 0.5%, and (iii) the reserve adjusted one-month LIBOR reset daily plus 1.0%, or (b) the reserve adjusted LIBOR for interest periods of one, two, three or six months, as selected by the Company, in each case plus an applicable margin.
Borrowings outstanding under the Credit Agreement						$ 0		$ 0		$ 0