Fair Value Measurements - Assets and Liabilities Not Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands		Dec. 31, 2016		Dec. 31, 2015
Financial Instruments Not Measured at Fair Value on Recurring Basis [Line items]
Securities Owned and Sold, Not yet Purchased, at Fair Value, Security Owned, Including Disposal Group Securities Owned		$ 710,668		$ 735,393
Fair value of the reverse repurchase agreements		24,006	[1]	206,499	[2]
Fair Value, Measurements, Nonrecurring [Member]
Financial Instruments Not Measured at Fair Value on Recurring Basis [Line items]
Cash		48,671		50,364
Deposits with clearing organization		11,748		18,034
Securities borrowed		154,090		224,672
Receivables from brokers		25,768		49,458
Securities failed to deliver		6,172		7,799
Clearing organizations		26,081		25,030
Other		2,823		58,832
Total Receivable from brokers, dealers and clearing organizations		214,934		365,791
Receivable from customers		847,386		840,355
Fair Value Estimate Not Practicable Mortgage Servicing Rights				41,838
Drafts payable		39,228		48,011
Bank call loans		145,800		100,200
Securities loaned		179,875		130,658
Fair Value Estimate Not Practicable Payable to Correspondent Brokers		610		3,316
Securities failed to receive		11,523		21,513
Other		29,381		9,059
Total payables to brokers, dealers and clearing organizations		221,389		164,546
Payables to customers		449,946		594,833
Securities sold under agreements to repurchase		378,084		651,445
Warehouse payable	[3]			54,341
Senior secured notes		151,782		154,568
Fair Value, Estimate Not Practicable, Investments		56,300		53,286
Level 1 | Fair Value, Measurements, Nonrecurring [Member]
Financial Instruments Not Measured at Fair Value on Recurring Basis [Line items]
Cash		48,671		50,364
Deposits with clearing organization		11,748		18,034
Drafts payable		39,228		48,011
Level 2
Financial Instruments Not Measured at Fair Value on Recurring Basis [Line items]
Fair value of the reverse repurchase agreements		24,006	[1]	206,499	[2]
Level 2 | Fair Value, Measurements, Nonrecurring [Member]
Financial Instruments Not Measured at Fair Value on Recurring Basis [Line items]
Securities borrowed		154,090		224,672
Receivables from brokers		25,768		49,458
Securities failed to deliver		6,172		7,799
Clearing organizations		26,081		25,030
Other		2,823		58,832
Total Receivable from brokers, dealers and clearing organizations		214,934		365,791
Receivable from customers		847,386		840,355
Bank call loans		145,800		100,200
Securities loaned		179,875		130,658
Fair Value Estimate Not Practicable Payable to Correspondent Brokers		610		3,316
Securities failed to receive		11,523		21,513
Other		29,381		9,059
Total payables to brokers, dealers and clearing organizations		221,389		164,546
Payables to customers		449,946		594,833
Securities sold under agreements to repurchase		378,084		651,445
Warehouse payable	[3]			54,341
Senior secured notes		151,782		154,568
Fair Value, Estimate Not Practicable, Investments		56,300		53,286
Level 3 | Fair Value, Measurements, Nonrecurring [Member]
Financial Instruments Not Measured at Fair Value on Recurring Basis [Line items]
Fair Value Estimate Not Practicable Mortgage Servicing Rights				41,838
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Nonrecurring [Member]
Financial Instruments Not Measured at Fair Value on Recurring Basis [Line items]
Fair Value, Estimate Not Practicable, Investments		56,300		53,286
Carrying Value | Fair Value, Measurements, Nonrecurring [Member]
Financial Instruments Not Measured at Fair Value on Recurring Basis [Line items]
Cash		48,671		50,364
Deposits with clearing organization		11,748		18,034
Securities borrowed		154,090		224,672
Receivables from brokers		25,768		49,458
Securities failed to deliver		6,172		7,799
Clearing organizations		26,081		25,030
Other		2,823		58,832
Total Receivable from brokers, dealers and clearing organizations		214,934		365,791
Receivable from customers		847,386		840,355
Fair Value Estimate Not Practicable Mortgage Servicing Rights				28,168
Drafts payable		39,228		48,011
Bank call loans		145,800		100,200
Securities loaned		179,875		130,658
Fair Value Estimate Not Practicable Payable to Correspondent Brokers		610		3,316
Securities failed to receive		11,523		21,513
Other		29,381		9,059
Total payables to brokers, dealers and clearing organizations		221,389		164,546
Payables to customers		449,946		594,833
Securities sold under agreements to repurchase		378,084		651,445
Warehouse payable	[3]			54,341
Senior secured notes		150,000		150,000
Fair Value, Estimate Not Practicable, Investments		$ 56,300		$ 53,286

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