Summary of Significant Accounting Policies - Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash paid:
Interest paid (net of amounts capitalized)	$ 11,165	$ 12,289	$ 16,749
Income Taxes Paid	3,891	11,286	105
Cash received:
Income taxes refund	1,600	6,985	7,768
Noncash investing and financing activities:
Acquisition of fixed assets included in accounts payable and accrued expenses	$ 455	$ 2,058	$ 2,031