Fair Value Measurements - Estimated Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Financial assets:
Held to maturity securities	$ 792,559	$ 276,296
Loans held for investment, net	7,852,463	7,788,552
Broker-dealer and clearing organization receivables	1,255,052	1,672,946
Financial liabilities:
Broker-dealer and clearing organization payables	1,176,156	1,477,300
Carrying Amount
Financial assets:
Cash and cash equivalents	1,778,247	2,823,523
Assets segregated for regulatory purposes	109,358	221,740
Securities purchased under agreements to resell	145,365	118,262
Held to maturity securities	889,452	267,684
Loans held for sale	140,178	95,599
Loans held for investment, net	7,843,551	7,788,552
Broker-dealer and clearing organization receivables	1,255,052	1,672,946
Other assets	71,365	73,041
Financial liabilities:
Deposits	11,352,014	12,818,077
Broker-dealer and clearing organization payables	1,176,156	1,477,300
Short-term borrowings	942,309	859,444
Debt	390,354	387,904
Other liabilities	9,198	3,944
Estimate of Fair Value
Financial assets:
Cash and cash equivalents	1,778,247	2,823,523
Assets segregated for regulatory purposes	109,358	221,740
Securities purchased under agreements to resell	145,365	118,262
Held to maturity securities	792,559	276,296
Loans held for sale	142,325	95,599
Loans held for investment, net	7,684,034	7,999,925
Broker-dealer and clearing organization receivables	1,255,052	1,672,946
Other assets	71,365	73,041
Financial liabilities:
Deposits	11,333,099	12,821,138
Broker-dealer and clearing organization payables	1,176,156	1,477,300
Short-term borrowings	942,309	859,444
Debt	389,632	387,904
Other liabilities	9,198	3,944
Estimate of Fair Value | Level 1
Financial assets:
Cash and cash equivalents	1,778,247	2,823,523
Assets segregated for regulatory purposes	109,358	221,740
Estimate of Fair Value | Level 2
Financial assets:
Securities purchased under agreements to resell	145,365	118,262
Held to maturity securities	792,559	276,296
Loans held for sale	85,137	95,599
Loans held for investment, net	402,502	733,193
Broker-dealer and clearing organization receivables	1,255,052	1,672,946
Other assets	69,699	71,290
Financial liabilities:
Deposits	11,333,099	12,821,138
Broker-dealer and clearing organization payables	1,176,156	1,477,300
Short-term borrowings	942,309	859,444
Debt	389,632	387,904
Other liabilities	9,198	3,944
Estimate of Fair Value | Level 3
Financial assets:
Loans held for sale	57,188
Loans held for investment, net	7,281,532	7,266,732
Other assets	$ 1,666	$ 1,751