Fair Value Measurements (Carrying Amounts and Estimated Fair Values of Financial Instruments Not Measured at Fair Value) (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Carrying Amount
Assets:
Cash and cash equivalents	$ 1,710,999	$ 1,467,129
Deposits with banks	38,459	36,209
Notes receivable, net	19,156	13,237
Secured financings receivable	352,013	76,311
Liabilities:
Secured financings payable	233,483	76,313
Notes and contracts payable	728,332	732,019
Estimated Fair Value
Assets:
Cash and cash equivalents	1,710,999	1,467,129
Deposits with banks	38,385	35,979
Notes receivable, net	19,029	12,805
Secured financings receivable	352,013	76,311
Liabilities:
Secured financings payable	233,483	76,313
Notes and contracts payable	762,011	741,839
Estimated Fair Value | Level 1
Assets:
Cash and cash equivalents	1,710,999	1,467,129
Deposits with banks	1,518	4,307
Notes receivable, net	0	0
Secured financings receivable	0	0
Liabilities:
Secured financings payable	0	0
Notes and contracts payable	0	0
Estimated Fair Value | Level 2
Assets:
Cash and cash equivalents	0	0
Deposits with banks	36,867	31,672
Notes receivable, net	0	0
Secured financings receivable	352,013	76,311
Liabilities:
Secured financings payable	233,483	76,313
Notes and contracts payable	757,739	736,048
Estimated Fair Value | Level 3
Assets:
Cash and cash equivalents	0	0
Deposits with banks	0	0
Notes receivable, net	19,029	12,805
Secured financings receivable	0	0
Liabilities:
Secured financings payable	0	0
Notes and contracts payable	$ 4,272	$ 5,791