Summary of Significant Accounting Principles (Details-1) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	$ 82,402	$ 83,102
Restricted cash	444	634
Receivable - margin account	1,570	1,193
Cash, cash equivalents, and restricted cash	84,416	84,929	$ 106,245	$ 112,094
MGE [Member]
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	9,624	4,843
Restricted cash	444	634
Receivable - margin account	1,570	1,193
Cash, cash equivalents, and restricted cash	$ 11,638	$ 6,670	$ 9,240	$ 10,093