Fair Value Measurements - Assets and Liabilities Not Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Receivable from brokers, dealers and clearing organizations:
Securities purchased under agreements to resell	$ 0	$ 251,606
Nonrecurring [Member]
Fair Value Measurement: Assets
Cash	46,983	32,632
Cash segregated for regulatory and other purposes	855	18,594
Deposits with clearing organization	17,873	12,322
Receivable from brokers, dealers and clearing organizations:
Securities borrowed	296,362	242,172
Receivables from brokers	53,550	38,149
Securities failed to deliver	16,380	11,055
Clearing organizations	23,766	21,106
Other	8,750	1,993
Total Receivable from brokers, dealers and clearing organizations	398,808	314,475
Receivable from customers	896,060	864,189
Securities purchased under agreements to resell		1,606
Mortgage servicing rights	43,750	42,279
Investments	48,032	50,548
Fair Value Measurement: Liabilities
Drafts payable	24,002	35,373
Bank call loans	147,700	59,400
Payables to brokers, dealers and clearing organizations:
Securities loaned	209,125	137,892
Payable to brokers	4,380	4,559
Securities failed to receive	31,266	23,573
Other	5,742	91,137
Total payables to brokers, dealers and clearing organizations	250,513	257,161
Payables to customers	692,416	652,256
Securities sold under agreements to repurchase	463,074	687,440
Warehouse payable	30,856	16,683
Senior secured notes	155,250	157,782
Level 1 [Member] | Nonrecurring [Member]
Fair Value Measurement: Assets
Cash	46,983	32,632
Cash segregated for regulatory and other purposes	855	18,594
Deposits with clearing organization	17,873	12,322
Receivable from brokers, dealers and clearing organizations:
Securities purchased under agreements to resell		1,606
Fair Value Measurement: Liabilities
Drafts payable	24,002	35,373
Level 2 [Member] | Nonrecurring [Member]
Receivable from brokers, dealers and clearing organizations:
Securities borrowed	296,362	242,172
Receivables from brokers	53,550	38,149
Securities failed to deliver	16,380	11,055
Clearing organizations	23,766	21,106
Other	8,750	1,993
Total Receivable from brokers, dealers and clearing organizations	398,808	314,475
Receivable from customers	896,060	864,189
Investments	48,032	50,548
Fair Value Measurement: Liabilities
Bank call loans	147,700	59,400
Payables to brokers, dealers and clearing organizations:
Securities loaned	209,125	137,892
Payable to brokers	4,380	4,559
Securities failed to receive	31,266	23,573
Other	5,742	91,137
Total payables to brokers, dealers and clearing organizations	250,513	257,161
Payables to customers	692,416	652,256
Securities sold under agreements to repurchase	463,074	687,440
Warehouse payable	30,856	16,683
Senior secured notes	155,250	157,782
Level 3 [Member] | Nonrecurring [Member]
Receivable from brokers, dealers and clearing organizations:
Mortgage servicing rights	43,750	42,279
Carrying Value [Member]
Fair Value Measurement: Assets
Deposits with clearing organization		12,322
Carrying Value [Member] | Nonrecurring [Member]
Fair Value Measurement: Assets
Cash	46,983	32,632
Cash segregated for regulatory and other purposes	855	18,594
Deposits with clearing organization	17,873
Receivable from brokers, dealers and clearing organizations:
Securities borrowed	296,362	242,172
Receivables from brokers	53,550	38,149
Securities failed to deliver	16,380	11,055
Clearing organizations	23,766	21,106
Other	8,750	1,993
Total Receivable from brokers, dealers and clearing organizations	398,808	314,475
Receivable from customers	896,060	864,189
Securities purchased under agreements to resell		1,606
Mortgage servicing rights	29,594	30,140
Investments	48,032	50,548
Fair Value Measurement: Liabilities
Drafts payable	24,002	35,373
Bank call loans	147,700	59,400
Payables to brokers, dealers and clearing organizations:
Securities loaned	209,125	137,892
Payable to brokers	4,380	4,559
Securities failed to receive	31,266	23,573
Other	5,742	91,137
Total payables to brokers, dealers and clearing organizations	250,513	257,161
Payables to customers	692,416	652,256
Securities sold under agreements to repurchase	463,074	687,440
Warehouse payable	30,856	16,683
Senior secured notes	150,000	150,000
Fair Value [Member]
Fair Value Measurement: Assets
Deposits with clearing organization		12,322
Fair Value [Member] | Nonrecurring [Member]
Fair Value Measurement: Assets
Cash	46,983	32,632
Cash segregated for regulatory and other purposes	855	18,594
Deposits with clearing organization	17,873
Receivable from brokers, dealers and clearing organizations:
Securities borrowed	296,362	242,172
Receivables from brokers	53,550	38,149
Securities failed to deliver	16,380	11,055
Clearing organizations	23,766	21,106
Other	8,750	1,993
Total Receivable from brokers, dealers and clearing organizations	398,808	314,475
Receivable from customers	896,060	864,189
Securities purchased under agreements to resell		1,606
Mortgage servicing rights	43,750	42,279
Investments	48,032	50,548
Fair Value Measurement: Liabilities
Drafts payable	24,002	35,373
Bank call loans	147,700	59,400
Payables to brokers, dealers and clearing organizations:
Securities loaned	209,125	137,892
Payable to brokers	4,380	4,559
Securities failed to receive	31,266	23,573
Other	5,742	91,137
Total payables to brokers, dealers and clearing organizations	250,513	257,161
Payables to customers	692,416	652,256
Securities sold under agreements to repurchase	463,074	687,440
Warehouse payable	30,856	16,683
Senior secured notes	$ 155,250	$ 157,782