Notes Payable, Collateralized and Short-Term Borrowings - Carrying Amounts and Estimated Fair Values of Company's Senior Notes (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Carrying amount of the Company's long-term debt	$ 948,911	$ 949,557
Estimated fair value of the Company's long-term debt	997,968	993,600
8.125% Senior Notes [Member]
Debt Instrument [Line Items]
Carrying amount of the Company's long-term debt	109,302	109,271
Estimated fair value of the Company's long-term debt	114,795	115,650
5.375% Senior Notes [Member]
Debt Instrument [Line Items]
Carrying amount of the Company's long-term debt	297,328	297,083
Estimated fair value of the Company's long-term debt	315,195	312,000
8.375% Senior Notes [Member]
Debt Instrument [Line Items]
Carrying amount of the Company's long-term debt	245,875	246,988
Estimated fair value of the Company's long-term debt	255,768	256,650
5.125% Senior Notes [Member]
Debt Instrument [Line Items]
Carrying amount of the Company's long-term debt	296,406	296,215
Estimated fair value of the Company's long-term debt	$ 312,210	$ 309,300