Fair Value Measurements (Carrying Amounts and Estimated Fair Values of Financial Instruments Not Measured at Fair Value) (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Carrying Amount
Assets:
Cash and cash equivalents	$ 1,953,987	$ 1,275,466
Deposits with banks	51,119	45,856
Notes receivable, net	38,204	29,912
Secured financings receivable	651,048	748,312
Liabilities:
Secured financings payable	593,607	516,155
Notes and contracts payable	1,648,863	1,010,756
Estimated Fair Value
Assets:
Cash and cash equivalents	1,953,987	1,275,466
Deposits with banks	51,235	45,947
Notes receivable, net	38,686	30,279
Secured financings receivable	651,048	748,312
Liabilities:
Secured financings payable	593,607	516,155
Notes and contracts payable	1,732,520	1,131,356
Estimated Fair Value | Level 1
Assets:
Cash and cash equivalents	1,953,987	1,275,466
Deposits with banks	8,362	6,092
Estimated Fair Value | Level 2
Assets:
Deposits with banks	42,873	39,855
Secured financings receivable	651,048	748,312
Liabilities:
Secured financings payable	593,607	516,155
Notes and contracts payable	1,728,170	1,125,128
Estimated Fair Value | Level 3
Assets:
Notes receivable, net	38,686	30,279
Liabilities:
Notes and contracts payable	$ 4,350	$ 6,228