Collateralized Transactions - Additional Information (Narrative) (Details) (USD $)	0 Months Ended	12 Months Ended
	Sep. 26, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Mar. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Bank call loans		$ 59,400,000		$ 118,200,000
Customer securities under customer margin loans available to be pledged		1,300,000,000
Customer securities under customer margin loans agreement available to be repledged		125,600,000
Customer securities deposited to secure obligations and margin requirements under option contracts		362,900,000
Outstanding letters of credit		0
Fair value of the reverse repurchase agreements		250,000,000	[1]	184,000,000	[1]
Fair value of the repurchase agreements		0
Carrying value of pledged securities owned that can be sold or re-pledged by the counterparty		518,100,000		586,600,000
Carrying value of securities owned by the Company loaned or pledged		149,100,000		126,800,000
Amount of first interim distribution	9,500,000
Fair value of the company's investment on reserves not paid in first distribution							600,000
Number of broker-dealers		2
Receivable from brokers and clearing organizations		101,600,000
Loans to Citizens		0
Credit Concentration Risk
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Guaranteed mortgages for a period		15 days
Interest expense		570,700		764,500		895,000
Warehouse Facility | Credit Concentration Risk
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding under the warehouse facility line		16,700,000		54,600,000
Reverse Repurchase Agreements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer securities under customer margin loans agreement available to be repledged		312,600,000		385,500,000
Securities received as collateral under securities borrowed transaction with market value		314,100,000		385,500,000
Securities Borrowed Transactions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer securities under customer margin loans agreement available to be repledged		4,400,000		11,000,000
Securities received as collateral under securities borrowed transaction with market value		235,100,000		265,300,000
Corporate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateralized loans, collateralized by firm		148,800,000
Other Than Corporate Customer
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Collateralized loans, collateralized by customer securities		$ 248,300,000

[1] Included in securities purchased under agreements to resell where the Company has elected fair value option treatment.