Fair Value Measurements (Carrying Amounts and Estimated Fair Values of Financial Instruments Not Measured at Fair Value) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Carrying Amount
Assets:
Cash and cash equivalents	$ 1,337,052	$ 1,467,129
Deposits with banks	45,062	36,209
Notes receivable, net	13,123	13,237
Secured financings receivable	127,640	76,311
Liabilities:
Secured financings payable	127,647	76,313
Notes and contracts payable	730,953	732,019
Estimated Fair Value
Assets:
Cash and cash equivalents	1,337,052	1,467,129
Deposits with banks	44,886	35,979
Notes receivable, net	13,007	12,805
Secured financings receivable	127,640	76,311
Liabilities:
Secured financings payable	127,647	76,313
Notes and contracts payable	750,436	741,839
Estimated Fair Value | Level 1
Assets:
Cash and cash equivalents	1,337,052	1,467,129
Deposits with banks	9,422	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	35,464	31,672
Notes receivable, net	0	0
Secured financings receivable	127,640	76,311
Liabilities:
Secured financings payable	127,647	76,313
Notes and contracts payable	745,001	736,048
Estimated Fair Value | Level 3
Assets:
Cash and cash equivalents	0	0
Deposits with banks	0	0
Notes receivable, net	13,007	12,805
Secured financings receivable	0	0
Liabilities:
Secured financings payable	0	0
Notes and contracts payable	$ 5,435	$ 5,791