Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Carrying Value
Fair Value of Financial Instruments
Liabilities - long-term debt (carried at cost)	$ 313,886	$ 284,699
Fair Value
Fair Value of Financial Instruments
Liabilities - long-term debt (carried at cost)	320,514	293,765
Recurring
Fair Value of Financial Instruments
Liabilities - long-term debt (carried at cost)	320,514	293,765
Significant other observable inputs (Level 2) | Recurring
Fair Value of Financial Instruments
Liabilities - long-term debt (carried at cost)	$ 320,514	$ 293,765