Cash, Cash Equivalents and Investment Debt Securities (Narrative) (Details) $ in Millions	Mar. 31, 2020 USD ($) security
Cash, Cash Equivalents, and Investment Debt Securities [Abstract]
Number of positions that were in a continuous unrealized loss position for more than twelve months \| security	90
Accrued investment income receivable \| $	$ 3.3

Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(4))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(10))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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