Adoption of Accounting Principles and Recently Issued Accounting Pronouncements (Details-1) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Standards Update 2016-18 - Restricted Cash [Member]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Restricted cash	$ 4,500	$ 5,100
Accounting Standards Update 2016-01 - Restricted Cash [Member]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Accumulated other comprehensive income (loss)	391
Accounting Standards Update 2016-01 - Restricted Cash [Member] | MGE [Member]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Accumulated other comprehensive income (loss)	$ (19)
Accounting Standards Update 2017-07 - Restricted Cash [Member]
Adoption of Accounting Principles and Recently Issued Accounting Pronouncements [Line Items]
Cumulative effect of new accounting guidance, retained earnings		$ 6,600	$ 5,000