Summary of Significant Accounting Policies (Details-2) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	$ 83,102,000	$ 107,952,000
Restricted cash	634,000	1,635,000
Receivable - margin account	1,193,000	2,507,000
Cash, cash equivalents, and restricted cash	84,929,000	112,094,000	$ 101,633,000	$ 86,694,000
MGE [Member]
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	4,843,000	5,951,000
Restricted cash	634,000	1,635,000
Receivable - margin account	1,193,000	2,507,000
Cash, cash equivalents, and restricted cash	$ 6,670,000	$ 10,093,000	$ 16,442,000	$ 32,070,000