Accrued Expenses, Other Current Liabilities and Other Long-Term Liabilities - Components of Other Long-term Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Capital lease obligations	$ 11,702	$ 11,589
Lease incentive obligations	2,779	2,652
Benefit plan obligations	2,161	2,060
Other	1,644	1,523
Total	$ 18,286	$ 17,824