Notes Payable, Other and Short-term Borrowings - Carrying Amounts and Estimated Fair Values of Company's Senior Notes (Parenthetical) (Detail)	Mar. 31, 2018	Dec. 31, 2017	May 27, 2016
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%
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%