Fair Value Measurements - Estimated Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Financial assets:
Held to maturity securities	$ 687,469	$ 649,872
Loans held for investment, net	7,860,580	7,849,435
Broker-dealer and clearing organization receivables	1,450,077	1,452,366
Financial liabilities:
Broker-dealer and clearing organization payables	1,446,886	1,331,902
Carrying Value
Financial assets:
Cash and cash equivalents	1,703,273	2,299,627
Assets segregated for regulatory purposes	88,451	70,963
Securities purchased under agreements to resell	99,099	88,728
Held to maturity securities	762,369	737,899
Loans held for sale	36,757	48,883
Loans held for investment, net	7,860,580	7,849,435
Broker-dealer and clearing organization receivables	1,450,077	1,452,366
Other assets	71,117	69,545
Financial liabilities:
Deposits	10,831,966	11,065,322
Broker-dealer and clearing organization payables	1,446,886	1,331,902
Short-term borrowings	705,008	834,023
Debt	198,043	347,667
Other liabilities	17,062	16,779
Fair Value
Financial assets:
Cash and cash equivalents	1,703,273	2,299,627
Assets segregated for regulatory purposes	88,451	70,963
Securities purchased under agreements to resell	99,099	88,728
Held to maturity securities	687,469	649,872
Loans held for sale	37,925	50,871
Loans held for investment, net	7,940,930	7,936,567
Broker-dealer and clearing organization receivables	1,450,077	1,452,366
Other assets	71,117	69,545
Financial liabilities:
Deposits	10,826,773	11,058,234
Broker-dealer and clearing organization payables	1,446,886	1,331,902
Short-term borrowings	705,008	834,023
Debt	187,183	331,965
Other liabilities	17,062	16,779
Fair Value | Level 1
Financial assets:
Cash and cash equivalents	1,703,273	2,299,627
Assets segregated for regulatory purposes	88,451	70,963
Fair Value | Level 2
Financial assets:
Securities purchased under agreements to resell	99,099	88,728
Held to maturity securities	687,469	649,872
Loans held for sale	4,325	1,436
Loans held for investment, net	324,223	363,718
Broker-dealer and clearing organization receivables	1,450,077	1,452,366
Other assets	71,117	69,545
Financial liabilities:
Deposits	10,826,773	11,058,234
Broker-dealer and clearing organization payables	1,446,886	1,331,902
Short-term borrowings	705,008	834,023
Debt	187,183	331,965
Other liabilities	17,062	16,779
Fair Value | Level 3
Financial assets:
Loans held for sale	33,600	49,435
Loans held for investment, net	$ 7,616,707	$ 7,572,849