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