Notes Payable, Collateralized and Short-Term Borrowings - Carrying Amounts and Estimated Fair Values of Company's Convertible Notes and Senior Notes (Parenthetical) (Detail)	Dec. 31, 2016	Jul. 15, 2016	Jul. 13, 2016	May 27, 2016	Dec. 31, 2015	Dec. 09, 2014	Jul. 29, 2011
4.50% Convertible Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	4.50%	4.50%	4.50%		4.50%		4.50%
8.125% Senior Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	8.125%				8.125%
5.375% Senior Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	5.375%				5.375%	5.375%
8.375% Senior Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	8.375%				8.375%
5.125% Senior Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	5.125%			5.125%	5.125%