Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 1,106	$ 1,100	$ 8,099
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	89,916	87,879	78,014
Deferred financing amortization	2,068	1,922	1,855
Employee retirement benefits	(8,103)	(3,634)	(12,078)
Provision for uncollectible receivables	4,031	3,648	3,590
Stock based compensation	2,303	1,584	4,174
Deferred income taxes	1,332	1,958	6,851
Changes in operating assets and liabilities:
Receivables	(4,672)	(3,722)	(1,731)
Material and supplies	409	838	(386)
Prepaid expenses and other current assets	(153)	9	(104)
Accounts payable and accrued expenses	3,935	(9,973)	3,882
Advance billings and customer deposits	(1,038)	8,565	(1,436)
Other current liabilities	(344)	(759)	(296)
Other	(702)	1,181	56
Net cash provided by operating activities	90,088	90,596	90,490
Cash flows from investing activities:
Capital expenditures	(97,841)	(99,034)	(96,706)
Proceeds on sale of investments		805	463
Net cash used in investing activities	(97,841)	(98,229)	(96,243)
Cash flows from financing activities:
Proceeds from exercise of warrant		6,870
Proceeds from installment financing	2,155	2,780	4,336
Repayment of capital lease and installment financing	(3,341)	(4,217)	(3,179)
Repayment of debt	(3,000)	(3,000)	(3,000)
Refinancing and loan amendment costs	(688)	(150)
Taxes paid related to net share settlement of equity awards	(364)	(948)	(1,520)
Net cash provided by (used in) financing activities	(5,238)	1,335	(3,363)
Net change in cash, cash equivalents and restricted cash	(12,991)	(6,298)	(9,116)
Cash, cash equivalents and restricted cash, beginning of period	34,137	40,435	49,551
Cash, cash equivalents and restricted cash, end of period	$ 21,146	$ 34,137	$ 40,435