Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurement- Fair Value and Carrying Value of Long-term Debt (Details)

v3.10.0.1
Fair Value Measurement- Fair Value and Carrying Value of Long-term Debt (Details) - USD ($)
Jun. 30, 2018
Dec. 31, 2017
Fair Value Disclosures [Abstract]    
Long-term debt value, fair value $ 214,553,000 $ 160,108,000
Long-term debt value, carrying value 214,508,000 160,598,000
Fair Value, Measurements, Nonrecurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value disclosure, nonrecurring $ 0 $ 0