Stockholders' Equity (Dividend Restrictions) (Details) - USD ($) $ / shares in Units, $ in Millions	Oct. 19, 2018	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Dividends payable		$ 6.0
Common Class A
Class of Stock [Line Items]
Common stock, dividends declared (in dollars per share)	$ 0.36
Common Class B
Class of Stock [Line Items]
Common stock, dividends declared (in dollars per share)	$ 0.18
Dividend Declared
Class of Stock [Line Items]
Dividends payable			$ 7.0
National Western Life Insurance Company
Class of Stock [Line Items]
Maximum dividend payment which may be paid without prior approval from Colorado Division of Insurance		$ 30.7