Fair Value of Financial Instruments (Carrying Amounts and Fair Values of Financial Instruments) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 1,041,259	$ 834,837
Accounts and accrued income receivable, net	291,607	236,895
Loans receivable, net	60,223	73,397
Deposits with banks	24,204	23,601
Available-for-sale investments at fair value	3,260,493	3,177,860
Notes receivable, net	9,927	9,953
Deposits	1,962,839	1,693,138
Accounts payable and accrued liabilities	361,730	406,819
Notes and contracts payable	458,571	301,007
Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	1,041,259	834,837
Accounts and accrued income receivable, net	291,607	236,895
Loans receivable, net	58,841	73,755
Deposits with banks	24,108	23,492
Notes receivable, net	10,108	10,542
Deposits	1,962,711	1,692,932
Accounts payable and accrued liabilities	361,730	406,819
Notes and contracts payable	454,681	310,285
Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	1,041,259	834,837
Accounts and accrued income receivable, net	291,607	236,895
Loans receivable, net	60,223	73,397
Deposits with banks	24,204	23,601
Notes receivable, net	9,927	9,953
Deposits	1,962,839	1,693,138
Accounts payable and accrued liabilities	361,730	406,819
Notes and contracts payable	458,571	301,007
Debt Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Available-for-sale investments at fair value	2,947,204	2,819,817
Debt Securities | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Available-for-sale investments at fair value	2,947,204	2,819,817
Debt Securities | Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Available-for-sale investments at fair value	2,947,204	2,819,817
Equity Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Available-for-sale investments at fair value	313,289	358,043
Equity Securities | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Available-for-sale investments at fair value	313,289	358,043
Equity Securities | Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Available-for-sale investments at fair value	$ 313,289	$ 358,043