Bank Loans (Schedule of Balance and Associated Percentage of Each Major Loan Category in Bank Loan Portfolio) (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total risk category of loan portfolio	$ 19,554,758		$ 19,441,467
Loans in process/(unapplied loan payments), net	(67,194)		1,108
Unamortized loan fees, net	(5,483)		(8,478)
Allowance for loan losses	(135,114)	$ (130,213)	(128,292)	$ (122,681)	$ (117,162)	$ (111,653)
Loans held for investment, net	$ 19,346,967		$ 19,305,805
Gross bank loans, Percent	100.00%		100.00%
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total risk category of loan portfolio	$ 8,253,851		$ 8,047,647
Allowance for loan losses	$ (11,242)	(12,507)	$ (13,855)	(14,413)	(22,696)	(20,441)
Gross bank loans, Percent	42.20%		41.40%
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total risk category of loan portfolio	$ 3,689,379		$ 3,566,987
Allowance for loan losses	$ (76,354)	(65,887)	$ (67,077)	(66,377)	(55,734)	(54,143)
Gross bank loans, Percent	18.90%		18.30%
Fund Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total risk category of loan portfolio	$ 3,346,785		$ 3,633,126
Allowance for loan losses	$ (12,179)	(8,763)	$ (10,173)	(12,178)	(12,943)	(11,711)
Gross bank loans, Percent	17.10%		18.70%
Securities-Based Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total risk category of loan portfolio	$ 2,253,045		$ 2,306,455
Allowance for loan losses	$ (2,813)	(3,068)	$ (3,035)	(3,086)	(3,117)	(3,157)
Gross bank loans, Percent	11.50%		11.90%
Construction And Land [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total risk category of loan portfolio	$ 1,198,395		$ 1,034,370
Allowance for loan losses	$ (16,379)	(18,589)	$ (11,817)	(12,645)	(10,317)	(8,568)
Gross bank loans, Percent	6.10%		5.30%
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total risk category of loan portfolio	$ 608,911		$ 660,631
Allowance for loan losses	$ (15,312)	(20,689)	$ (21,386)	(13,429)	(11,566)	(12,897)
Gross bank loans, Percent	3.10%		3.40%
Home Equity Lines Of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total risk category of loan portfolio	$ 158,472		$ 136,270
Allowance for loan losses	$ (362)	(246)	$ (371)	(168)	(412)	(364)
Gross bank loans, Percent	0.80%		0.70%
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total risk category of loan portfolio	$ 45,920		$ 55,981
Allowance for loan losses	$ (473)	$ (464)	$ (578)	$ (385)	$ (377)	$ (372)
Gross bank loans, Percent	0.30%		0.30%