Fair Value Measurements - Fair Value Methods Used for Measuring Fair Values of Financial Instruments on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
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	$ 659,999	$ 551,938
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	310,039	208,818
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 - maturity less than 1 year	119,347	54,388
Debt securities - maturity 1 to 5 years	212,205	277,514
Debt securities - maturity greater than 5 years	18,408	11,218
Mortgage Loans Held-For-Sale, net	$ 86,429	$ 119,953