Note 1 - Condensed Consolidated Financial Statements - Business Overview, Recent Developments and Significant Accounting Policies Business Overview (Details) $ in Billions	9 Months Ended
	Sep. 30, 2018 USD ($) segment
Business Overview [Abstract]
Number of Reportable Business Segments | segment	2
Mortgage Insurance Segment
Mortgage Insurance [Abstract]
Private Mortgage Insurance Protects Lenders For Loans Made With Less Than This Maximum Down Payment Percentage	20.00%
Private Mortgage Insurance Protects Lenders For Refinancings Made to Home Buyers With Less Than This Maximum Equity-Ownership Percentage	20.00%
Mortgage Insurance Segment | Total primary reserves
Mortgage Insurance [Abstract]
Direct Primary Mortgage Insurance RIF | $	$ 55.6