Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income (loss)	$ (107,241)	$ 1,106	$ 1,100
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	88,424	89,916	87,879
Deferred financing amortization	1,442	2,068	1,922
Loss on early extinguishment of debt	4,826
Employee retirement benefits	(1,720)	(8,103)	(3,634)
Provision for uncollectible receivables	3,797	4,031	3,648
Stock based compensation	2,827	2,303	1,584
Deferred income taxes	88,628	1,332	1,958
Changes in operating assets and liabilities:
Receivables	(2,649)	(4,672)	(3,722)
Material and supplies	1,280	409	838
Prepaid expenses and other current assets	95	(153)	9
Accounts payable and accrued expenses	(1,059)	3,935	(9,973)
Advance billings and customer deposits	20,377	(1,038)	8,565
Other current liabilities	(653)	(344)	(759)
Other	336	(702)	1,181
Net cash provided by operating activities	98,710	90,088	90,596
Cash flows from investing activities:
Capital expenditures	(95,256)	(97,841)	(99,034)
Proceeds on sale of investments			805
Net cash used in investing activities	(95,256)	(97,841)	(98,229)
Cash flows from financing activities:
Proceeds from borrowing	330,000
Proceeds from exercise of warrant			6,870
Proceeds from installment financing	2,423	2,155	2,780
Repayment of capital lease and installment financing	(3,961)	(3,341)	(4,217)
Repayment of borrowings	(305,263)	(3,000)	(3,000)
Refinancing and loan amendment costs	(6,295)	(688)	(150)
Taxes paid related to net share settlement of equity awards	(495)	(364)	(948)
Net cash provided by (used in) financing activities	16,409	(5,238)	1,335
Net change in cash, cash equivalents and restricted cash	19,863	(12,991)	(6,298)
Cash, cash equivalents and restricted cash, beginning of period	21,146	34,137	40,435
Cash, cash equivalents and restricted cash, end of period	$ 41,009	$ 21,146	$ 34,137