Commitments and Contingencies Information Regarding Other Commitments (Details 4) - USD ($) $ in Thousands	3 Months Ended
Dec. 31, 2017	Mar. 31, 2018
Investment In Limited Partnerships [Member]
Other Commitments [Line Items]
Other Commitment		$ 44,846
Proprietary Funds [Member]
Other Commitments [Line Items]
Other Commitment		100,000
Financial Guard LLC [Member]
Other Commitments [Line Items]
Other Commitment		$ 5,000
Other Commitment, Amount Paid	$ 2,500

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

No definition available.

Name:	us-gaap_OtherCommitment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant