Fair Value Measurements - Assets and Liabilities Not Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Securities purchased under agreements to resell	$ 104,301	$ 251,606
Nonrecurring [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Cash	49,747	32,632
Fair Value Estimate Not Practicable Cash And Securities Segregated Under Federal And Other Regulations	855	18,594
Fair Value Estimate Not Practicable Deposits With Clearing Organizations	23,435	12,322
Deposits paid for securities borrowed	279,695	242,172
Receivables from brokers	19,867	38,149
Securities failed to deliver	16,723	11,055
Clearing organizations	23,265	21,106
Other	17,620	1,993
Total Receivable from brokers, dealers and clearing organizations	357,170	314,475
Receivable from customers	905,387	864,189
Securities purchased under agreements to resell		1,606
Mortgage servicing rights (MSRs)	41,414	42,279
Drafts payable	4,054	35,373
Bank call loans	177,500	59,400
Deposits received for securities loaned	209,226	137,892
Fair Value Estimate Not Practicable Payable To Correspondent Brokers	6,454	4,559
Securities failed to receive	20,491	23,573
Clearing organizations and other	1,836	91,137
Total payables to brokers, dealers and clearing organizations	238,007	257,161
Payables to customers	654,241	652,256
Securities sold under agreements to repurchase	623,852	687,440
Warehouse payable	70,860	16,683
Senior secured notes	156,563	157,782
Level 1 [Member] | Nonrecurring [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Cash	49,747	32,632
Fair Value Estimate Not Practicable Cash And Securities Segregated Under Federal And Other Regulations	855	18,594
Fair Value Estimate Not Practicable Deposits With Clearing Organizations	23,435	12,322
Securities purchased under agreements to resell		1,606
Drafts payable	4,054	35,373
Level 2 [Member] | Nonrecurring [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Deposits paid for securities borrowed	279,695	242,172
Receivables from brokers	19,867	38,149
Securities failed to deliver	16,723	11,055
Clearing organizations	23,265	21,106
Other	17,620	1,993
Total Receivable from brokers, dealers and clearing organizations	357,170	314,475
Receivable from customers	905,387	864,189
Bank call loans	177,500	59,400
Deposits received for securities loaned	209,226	137,892
Fair Value Estimate Not Practicable Payable To Correspondent Brokers	6,454	4,559
Securities failed to receive	20,491	23,573
Clearing organizations and other	1,836	91,137
Total payables to brokers, dealers and clearing organizations	238,007	257,161
Payables to customers	654,241	652,256
Securities sold under agreements to repurchase	623,852	687,440
Warehouse payable	70,860	16,683
Senior secured notes	156,563	157,782
Level 3 [Member] | Nonrecurring [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Mortgage servicing rights (MSRs)	41,414	42,279
Carrying Value [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Fair Value Estimate Not Practicable Deposits With Clearing Organizations		12,322
Carrying Value [Member] | Nonrecurring [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Cash	49,747	32,632
Fair Value Estimate Not Practicable Cash And Securities Segregated Under Federal And Other Regulations	855	18,594
Fair Value Estimate Not Practicable Deposits With Clearing Organizations	23,435
Deposits paid for securities borrowed	279,695	242,172
Receivables from brokers	19,867	38,149
Securities failed to deliver	16,723	11,055
Clearing organizations	23,265	21,106
Other	17,620	1,993
Total Receivable from brokers, dealers and clearing organizations	357,170	314,475
Receivable from customers	905,387	864,189
Securities purchased under agreements to resell		1,606
Mortgage servicing rights (MSRs)	29,220	30,140
Drafts payable	4,054	35,373
Bank call loans	177,500	59,400
Deposits received for securities loaned	209,226	137,892
Fair Value Estimate Not Practicable Payable To Correspondent Brokers	6,454	4,559
Securities failed to receive	20,491	23,573
Clearing organizations and other	1,836	91,137
Total payables to brokers, dealers and clearing organizations	238,007	257,161
Payables to customers	654,241	652,256
Securities sold under agreements to repurchase	623,852	687,440
Warehouse payable	70,860	16,683
Senior secured notes	150,000	150,000
Fair Value [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Fair Value Estimate Not Practicable Deposits With Clearing Organizations		12,322
Fair Value [Member] | Nonrecurring [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Cash	49,747	32,632
Fair Value Estimate Not Practicable Cash And Securities Segregated Under Federal And Other Regulations	855	18,594
Fair Value Estimate Not Practicable Deposits With Clearing Organizations	23,435
Deposits paid for securities borrowed	279,695	242,172
Receivables from brokers	19,867	38,149
Securities failed to deliver	16,723	11,055
Clearing organizations	23,265	21,106
Other	17,620	1,993
Total Receivable from brokers, dealers and clearing organizations	357,170	314,475
Receivable from customers	905,387	864,189
Securities purchased under agreements to resell		1,606
Mortgage servicing rights (MSRs)	41,414	42,279
Drafts payable	4,054	35,373
Bank call loans	177,500	59,400
Deposits received for securities loaned	209,226	137,892
Fair Value Estimate Not Practicable Payable To Correspondent Brokers	6,454	4,559
Securities failed to receive	20,491	23,573
Clearing organizations and other	1,836	91,137
Total payables to brokers, dealers and clearing organizations	238,007	257,161
Payables to customers	654,241	652,256
Securities sold under agreements to repurchase	623,852	687,440
Warehouse payable	70,860	16,683
Senior secured notes	$ 156,563	$ 157,782