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Fair Value Measurements - Narrative (Details) - USD ($)	9 Months Ended
Fair Value Measurements - Narrative (Details) - USD ($)	Sep. 30, 2016	Dec. 31, 2015	Apr. 12, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liability, Fair Value	$ 1,413,000	$ 14,162,000
Derivative Liability, Notional Amount	5,505,328,000	3,268,047,000
Principal	120,479,000
Securities owned, including amounts pledged of $799,379 ($546,334 in 2015), at fair value	1,027,933,000	734,831,000
Auction Rate Securities Committed To Purchase related to settlements with regulators	3,000,000
Auction rate securities, firm purchased and hold	92,000,000
Amount of ARS committed to purchase from clients	25,500,000
Valuation adjustment (unrealized loss) for ARS	$ (1,387,000)
Interest rate	8.75%		8.75%
Forward or delayed delivery of the underlying instrument with settlement (in days)	180 days
Fair Value Of Level Three Assets	$ 119,092,000
Student Loan Auction Rate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
U S Treasury Rate	1.42%
Maximum [Member] \| Auction Rate Preferred Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
U S Treasury Rate	1.42%
Maximum [Member] \| LIBOR or Treasury Yield [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Auction market preferred securities variable interest rate earned	200.00%
Minimum [Member] \| Auction Rate Preferred Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
U S Treasury Rate	1.01%
Auction Rate Securities [Member] \| Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commitment to purchase ARS period maximum	2020
Auction Rate Securities Purchase Commitment [Member] \| Municipal Auction Rate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Principal	$ 1,000
Valuation adjustment (unrealized loss) for ARS	0
Fair Value Of Level Three Assets	$ 1,000
Valuation Technique	Discounted Cash Flow
Auction Rate Securities Purchase Commitment [Member] \| Student Loan Auction Rate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Principal	$ 21,000
Valuation adjustment (unrealized loss) for ARS	(1,000)
Fair Value Of Level Three Assets	$ 20,000
Valuation Technique	Discounted Cash Flow
Mortgage Servicing Rights [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Permanent and construction loans , discount rate	12.00%
Continuous prepayment rate used up to loans prepayment penalty rate hit 4%	0.00%
Continuous prepayment rate	4.00%
Continuous prepayment rate vast majority range minimum	10.00%
Continuous prepayment rate vast majority range maximum	15.00%
Continuous prepayment rate vast majority range average rate	12.00%
Estimated future cost to service loans on an annual basis per loan, average	$ 1,250
Auction Rate Preferred Securities and Municipal Auction Rate Securities [Member] \| Auction Rate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Valuation adjustment (unrealized loss) for ARS	(276,000)
Auction Rate Securities Purchase Commitment [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Principal	28,454,000
Valuation adjustment (unrealized loss) for ARS	629,000
Fair Value Of Level Three Assets	29,083,000
Auction Rate Securities Purchase Commitment [Member] \| Auction Rate Preferred Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Principal	$ 6,512,000
Duration	4 years
Valuation adjustment (unrealized loss) for ARS	$ 905,000
Fair Value Of Level Three Assets	$ 7,417,000
Valuation Technique	Discounted Cash Flow
Auction Rate Securities Purchase Commitment [Member] \| Municipal Auction Rate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	1.41%
Permanent and construction loans , discount rate	1.89%
Duration	4 years 6 months
Auction Rate Securities Purchase Commitment [Member] \| Student Loan Auction Rate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	1.73%
Permanent and construction loans , discount rate	2.62%
Duration	7 years
Auction Rate Securities Purchase Commitment [Member] \| Weighted Average [Member] \| Auction Rate Preferred Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	1.11%
Permanent and construction loans , discount rate	1.54%
Duration	4 years
Auction Rate Securities Purchase Commitment [Member] \| Weighted Average [Member] \| Municipal Auction Rate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	1.41%
Permanent and construction loans , discount rate	1.89%
Duration	4 years 6 months
Auction Rate Securities Purchase Commitment [Member] \| Weighted Average [Member] \| Student Loan Auction Rate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	1.73%
Permanent and construction loans , discount rate	2.62%
Duration	7 years
Auction Rate Securities Purchase Commitment [Member] \| Maximum [Member] \| Auction Rate Preferred Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	1.40%
Permanent and construction loans , discount rate	1.56%
Auction Rate Securities Purchase Commitment [Member] \| Minimum [Member] \| Auction Rate Preferred Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	0.80%
Permanent and construction loans , discount rate	1.52%
Auction Rate Securities Owned [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Principal	$ 92,025,000
Valuation adjustment (unrealized loss) for ARS	(2,016,000)
Fair Value Of Level Three Assets	90,009,000
Auction Rate Securities Owned [Member] \| Auction Rate Preferred Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Principal	$ 88,100,000
Duration	4 years
Valuation adjustment (unrealized loss) for ARS	$ (1,665,000)
Fair Value Of Level Three Assets	$ 86,435,000
Valuation Technique	Discounted Cash Flow
Auction Rate Securities Owned [Member] \| Student Loan Auction Rate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	1.73%
Principal	$ 300,000
Permanent and construction loans , discount rate	2.62%
Duration	7 years
Valuation adjustment (unrealized loss) for ARS	$ (17,000)
Fair Value Of Level Three Assets	$ 283,000
Valuation Technique	Discounted Cash Flow
Auction Rate Securities Owned [Member] \| Weighted Average [Member] \| Auction Rate Preferred Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	1.11%
Permanent and construction loans , discount rate	1.54%
Duration	4 years
Auction Rate Securities Owned [Member] \| Weighted Average [Member] \| Student Loan Auction Rate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	1.73%
Permanent and construction loans , discount rate	2.62%
Duration	7 years
Auction Rate Securities Owned [Member] \| Maximum [Member] \| Auction Rate Preferred Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	1.40%
Permanent and construction loans , discount rate	1.56%
Auction Rate Securities Owned [Member] \| Minimum [Member] \| Auction Rate Preferred Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current Yield	0.80%
Permanent and construction loans , discount rate	1.52%
Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member] \| Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities owned, including amounts pledged of $799,379 ($546,334 in 2015), at fair value	$ 14,200,000	$ 14,000,000