Fair Value of Financial Instruments (Fair Value of Financial Instruments, Classified Using Three-Level Hierarchy) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 770,420	$ 834,837
Accounts and accrued income receivable, net	242,541	236,895
Loans receivable, net	70,733	73,397
Deposits with banks	22,832	23,601
Available-for-sale investments at fair value	3,172,274	3,177,860
Notes receivable, net	9,361	9,953
Deposits	1,762,458	1,693,138
Accounts payable and accrued liabilities	316,016	406,819
Notes and contracts payable	455,824	301,007
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	770,420	834,837
Accounts and accrued income receivable, net	242,541	236,895
Loans receivable, net
Deposits with banks	3,773	2,070
Available-for-sale investments at fair value	346,797	358,043
Notes receivable, net
Deposits	1,738,944	1,666,336
Accounts payable and accrued liabilities	316,016	406,819
Notes and contracts payable
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents
Accounts and accrued income receivable, net
Loans receivable, net
Deposits with banks	19,059	21,531
Available-for-sale investments at fair value	2,806,831	2,800,795
Notes receivable, net
Deposits	23,514	26,802
Accounts payable and accrued liabilities
Notes and contracts payable	449,677	294,221
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents
Accounts and accrued income receivable, net
Loans receivable, net	70,733	73,397
Deposits with banks
Available-for-sale investments at fair value	18,646	19,022
Notes receivable, net	9,361	9,953
Deposits
Accounts payable and accrued liabilities
Notes and contracts payable	6,147	6,786
Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale investments at fair value	2,825,477	2,819,817
Debt Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale investments at fair value
Debt Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale investments at fair value	2,806,831	2,800,795
Debt Securities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale investments at fair value	18,646	19,022
Equity Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale investments at fair value	346,797	358,043
Equity Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale investments at fair value	346,797	358,043
Equity Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale investments at fair value
Equity Securities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale investments at fair value