7. Stockholders' Equity (Details) - shares	3 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common Class A [Member]
Class of Stock [Line Items]
Shares, Issued		24,679,000	24,454,000	24,230,000	23,972,000
Stock Issued During Period, Shares, Conversion of Convertible Securities		34,000	13,000	18,000
Stock Issued During Period, Shares, New Issues		191,000	211,000	240,000
Common Stock, Voting Rights		.10
Election Percentage for Board of Directors		25.00%
Common Class B [Member]
Class of Stock [Line Items]
Shares, Issued		5,108,000	5,124,000	5,131,000	5,099,000
Stock Issued During Period, Shares, Conversion of Convertible Securities		(34,000)	(13,000)	(18,000)
Stock Issued During Period, Shares, New Issues		18,000	6,000	50,000
Common Stock, Voting Rights		1
Election Percentage for Board of Directors		75.00%
Treasury Class-A [Member]
Class of Stock [Line Items]
Treasury Stock, Shares, Acquired	122	13,200
Treasury Class B [Member]
Class of Stock [Line Items]
Treasury Stock, Shares, Acquired	917