Investments Investment Deposits and Payables (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Invested assets on deposit with state regulatory authorities	$ 7.1	$ 7.0
Payable for investments purchased	$ 1.0	$ 0.6

Carrying amount of cash and investment securities on deposit with state regulatory authorities in connection with capital requirements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 320
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75027294&loc=d3e22002-158495

Name:	us-gaap_AssetsHeldByInsuranceRegulators
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant