Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Aug. 18, 2015
Total debt
Long-term debt	$ 35,287	$ 36,365
Amounts payable within one year	10,287	0
Long-term debt, noncurrent	25,000	35,287
Revolving credit facility [Member]
Total debt
Long-term debt	35,287	35,287	$ 100,000
Secured debt of affiliate [Member]
Total debt
Long-term debt	$ 0	$ 1,078