Business Acquisitions Business Acquisition (Assets Liabilities Acquired) (Details) members in Thousands, medical_member in Millions	Sep. 30, 2017 members medical_member counties
Business Acquisition [Line Items]
Number of members to be served after acquisition of HealthSun Health Plans Inc | medical_member	40.3
America’s 1st Choice [Member]
Business Acquisition [Line Items]
Number of medical members to be acquired	130
HealthSun Health Plans Inc [Member]
Business Acquisition [Line Items]
Number of medical members to be acquired	40
State of Florida [Member]
Business Acquisition [Line Items]
Number of members to be served after acquisition of HealthSun Health Plans Inc	650
State of Florida [Member] | America’s 1st Choice [Member]
Business Acquisition [Line Items]
Number Of Counties In Which Entity Operates | counties	25
State of South Carolina [Member] | America’s 1st Choice [Member]
Business Acquisition [Line Items]
Number Of Counties In Which Entity Operates | counties	3