CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common Stock
Common stock, par value (USD per share)	$ 0.001	$ 0.001
Class B Convertible Common Stock
Common stock, par value (USD per share)	0.001	0.001
Common Stock | Common Stock
Common stock, par value (USD per share)	1.000	1.000	$ 1.000
Common Stock | Class B Convertible Common Stock
Common stock, par value (USD per share)	$ 1.000	$ 1.000	$ 1.000