Fair Value Measurements - Fair Value Methods Used for Measuring the Fair Values of Financial Instruments on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Total available-for-sale securities	$ 536,720	$ 519,943
Level 1 [Member]
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Equity securities	204,377	160,021
Level 2 [Member]
Fair Value Assumption, Date of Securitization or Asset-backed Financing Arrangement, Transferor's Continuing Involvement, Servicing Assets or Liabilities [Line Items]
Debt securities	332,343	359,922
Mortgage Loans Held-For-Sale, net	$ 86,648	$ 78,335