Collateralized Transactions - Maturities Schedule (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	$ 1,418,279	$ 1,641,320
Overnight
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	518,279	781,320
0 - 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	635,000	410,000
31 - 60 days
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	150,000	325,000
61 - 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	115,000	125,000
Securities loaned
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	463,377	707,744
Securities loaned | Overnight
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	463,377	707,744
Securities loaned | 0 - 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	0	0
Securities loaned | 31 - 60 days
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	0	0
Securities loaned | 61 - 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	0	0
Financial instruments sold under agreements to repurchase
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	954,902	933,576
Financial instruments sold under agreements to repurchase | Overnight
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	54,902	73,576
Financial instruments sold under agreements to repurchase | 0 - 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	635,000	410,000
Financial instruments sold under agreements to repurchase | 31 - 60 days
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	150,000	325,000
Financial instruments sold under agreements to repurchase | 61 - 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Assets sold under agreements to repurchase	$ 115,000	$ 125,000