Notes Payable, Collateralized and Short-Term Borrowings - Summary of Company's Convertible Notes (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) shares $ / shares	Dec. 31, 2014 USD ($) shares $ / shares	Jul. 29, 2011 USD ($)	Apr. 01, 2010 USD ($)
Debt Instrument [Line Items]
Carrying amount of debt component	$ 891,200,000	$ 706,700,000
4.50% Convertible Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt component	160,000,000	160,000,000	$ 160,000,000
Unamortized discount	(5,089,000)	(7,473,000)
Carrying amount of debt component	154,911,000	152,527,000
Equity component	$ 18,972,000	$ 18,972,000
Effective interest rate	7.61%	7.61%
Maturity date (period through which discount is being amortized)	Jul. 15, 2016	Jul. 15, 2016
Conversion price | $ / shares	$ 9.84	$ 9.84
Number of shares to be delivered upon conversion | shares	16,260,160	16,260,160
8.75% Convertible Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt component		$ 150,000,000		$ 150,000,000
Carrying amount of debt component		$ 150,000,000
Effective interest rate	0.00%	8.75%
Maturity date (period through which discount is being amortized)	Apr. 15, 2015	Apr. 15, 2015
Conversion price | $ / shares		$ 6.25
Number of shares to be delivered upon conversion | shares		23,990,604
Amount by which the notes' if-converted value exceeds their principal amount		$ 69,514,000