Fair Value Measurements (Carrying Amounts and Estimated Fair Values of Financial Instruments Not Measured at Fair Value) (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Carrying Amount
Assets:
Cash and cash equivalents	$ 2,026,024	$ 1,275,466
Deposits with banks	45,359	45,856
Notes receivable, net	39,355	29,912
Secured financings receivable	745,813	748,312
Liabilities:
Secured financings payable	645,530	516,155
Notes and contracts payable	1,009,447	1,010,756
Estimated Fair Value
Assets:
Cash and cash equivalents	2,026,024	1,275,466
Deposits with banks	45,947	45,947
Notes receivable, net	39,613	30,279
Secured financings receivable	745,813	748,312
Liabilities:
Secured financings payable	645,530	516,155
Notes and contracts payable	1,102,170	1,131,356
Estimated Fair Value | Level 1
Assets:
Cash and cash equivalents	2,026,024	1,275,466
Deposits with banks	6,092	6,092
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	39,855	39,855
Notes receivable, net	0	0
Secured financings receivable	745,813	748,312
Liabilities:
Secured financings payable	645,530	516,155
Notes and contracts payable	1,096,598	1,125,128
Estimated Fair Value | Level 3
Assets:
Cash and cash equivalents	0	0
Deposits with banks	0	0
Notes receivable, net	39,613	30,279
Secured financings receivable	0	0
Liabilities:
Secured financings payable	0	0
Notes and contracts payable	$ 5,572	$ 6,228