Fair Value Measurements - Assets and Liabilities Not Measured at Fair Value on Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Securities purchased under agreements to resell	$ 0	$ 251,606
Nonrecurring [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Cash	38,843	32,632
Fair Value Estimate Not Practicable Cash And Securities Segregated Under Federal And Other Regulations	1,517	18,594
Fair Value Estimate Not Practicable Deposits With Clearing Organizations	22,064	12,322
Deposits paid for securities borrowed	266,563	242,172
Receivables from brokers	25,663	38,149
Securities failed to deliver	19,248	11,055
Clearing organizations	23,857	21,106
Other	2,772	1,993
Total Receivable from brokers, dealers and clearing organizations	338,103	314,475
Receivable from customers	890,260	864,189
Securities purchased under agreements to resell		1,606
Mortgage servicing rights (MSRs)	40,772	42,279
Drafts payable	34,615	35,373
Bank call loans	101,400	59,400
Deposits received for securities loaned	165,005	137,892
Fair Value Estimate Not Practicable Payable To Correspondent Brokers	7,347	4,559
Securities failed to receive	18,557	23,573
Clearing organizations and other	159,321	91,137
Total payables to brokers, dealers and clearing organizations	350,230	257,161
Payables to customers	704,087	652,256
Securities sold under agreements to repurchase	397,389	687,440
Warehouse payable	87,562	16,683
Senior secured notes	157,407	157,782
Level 1 [Member] | Nonrecurring [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Cash	38,843	32,632
Fair Value Estimate Not Practicable Cash And Securities Segregated Under Federal And Other Regulations	1,517	18,594
Fair Value Estimate Not Practicable Deposits With Clearing Organizations	22,064	12,322
Securities purchased under agreements to resell		1,606
Drafts payable	34,615	35,373
Level 2 [Member] | Nonrecurring [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Deposits paid for securities borrowed	266,563	242,172
Receivables from brokers	25,663	38,149
Securities failed to deliver	19,248	11,055
Clearing organizations	23,857	21,106
Other	2,772	1,993
Total Receivable from brokers, dealers and clearing organizations	338,103	314,475
Receivable from customers	890,260	864,189
Bank call loans	101,400	59,400
Deposits received for securities loaned	165,005	137,892
Fair Value Estimate Not Practicable Payable To Correspondent Brokers	7,347	4,559
Securities failed to receive	18,557	23,573
Clearing organizations and other	159,321	91,137
Total payables to brokers, dealers and clearing organizations	350,230	257,161
Payables to customers	704,087	652,256
Securities sold under agreements to repurchase	397,389	687,440
Warehouse payable	87,562	16,683
Senior secured notes	157,407	157,782
Level 3 [Member] | Nonrecurring [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Mortgage servicing rights (MSRs)	40,772	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	38,843	32,632
Fair Value Estimate Not Practicable Cash And Securities Segregated Under Federal And Other Regulations	1,517	18,594
Fair Value Estimate Not Practicable Deposits With Clearing Organizations	22,064
Deposits paid for securities borrowed	266,563	242,172
Receivables from brokers	25,663	38,149
Securities failed to deliver	19,248	11,055
Clearing organizations	23,857	21,106
Other	2,772	1,993
Total Receivable from brokers, dealers and clearing organizations	338,103	314,475
Receivable from customers	890,260	864,189
Securities purchased under agreements to resell		1,606
Mortgage servicing rights (MSRs)	28,391	30,140
Drafts payable	34,615	35,373
Bank call loans	101,400	59,400
Deposits received for securities loaned	165,005	137,892
Fair Value Estimate Not Practicable Payable To Correspondent Brokers	7,347	4,559
Securities failed to receive	18,557	23,573
Clearing organizations and other	159,321	91,137
Total payables to brokers, dealers and clearing organizations	350,230	257,161
Payables to customers	704,087	652,256
Securities sold under agreements to repurchase	397,389	687,440
Warehouse payable	87,562	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	38,843	32,632
Fair Value Estimate Not Practicable Cash And Securities Segregated Under Federal And Other Regulations	1,517	18,594
Fair Value Estimate Not Practicable Deposits With Clearing Organizations	22,064
Deposits paid for securities borrowed	266,563	242,172
Receivables from brokers	25,663	38,149
Securities failed to deliver	19,248	11,055
Clearing organizations	23,857	21,106
Other	2,772	1,993
Total Receivable from brokers, dealers and clearing organizations	338,103	314,475
Receivable from customers	890,260	864,189
Securities purchased under agreements to resell		1,606
Mortgage servicing rights (MSRs)	40,772	42,279
Drafts payable	34,615	35,373
Bank call loans	101,400	59,400
Deposits received for securities loaned	165,005	137,892
Fair Value Estimate Not Practicable Payable To Correspondent Brokers	7,347	4,559
Securities failed to receive	18,557	23,573
Clearing organizations and other	159,321	91,137
Total payables to brokers, dealers and clearing organizations	350,230	257,161
Payables to customers	704,087	652,256
Securities sold under agreements to repurchase	397,389	687,440
Warehouse payable	87,562	16,683
Senior secured notes	$ 157,407	$ 157,782