UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating revenue:
Operating revenues	$ 158,914	$ 156,501	$ 317,757	$ 310,639
Operating expenses:
Selling, general and administrative	27,170	29,915	55,892	58,665
Depreciation and amortization	42,353	41,117	83,532	84,604
Total operating expenses	134,894	135,332	268,950	272,716
Operating income	24,020	21,169	48,807	37,923
Other income (expense):
Interest expense	(7,522)	(8,851)	(15,476)	(18,183)
Other	1,176	839	2,463	1,828
Income before income taxes	17,674	13,157	35,794	21,568
Income tax expense	4,524	3,531	8,734	5,359
Net income	13,150	9,626	27,060	16,209
Other comprehensive income (loss):
Unrealized gain (loss) on interest rate hedge, net of tax	(4,212)		(6,940)
Unrealized gain (loss) on interest rate hedge, net of tax		833		3,895
Comprehensive income	$ 8,938	$ 10,459	$ 20,120	$ 20,104
Net income per share, basic and diluted:
Basic net income per share (in dollars per share)	$ 0.26	$ 0.19	$ 0.54	$ 0.33
Diluted net income per share (in dollars per share)	$ 0.26	$ 0.19	$ 0.54	$ 0.32
Weighted average shares outstanding, basic (in shares)	49,848	49,547	49,812	49,511
Weighted average shares outstanding, diluted (in shares)	50,142	50,070	50,118	50,029
Service revenue and other
Operating revenue:
Operating revenues	$ 142,059	$ 140,492	$ 285,290	$ 277,051
Equipment revenue
Operating revenue:
Operating revenues	16,855	16,009	32,467	33,588
Cost of services
Operating expenses:
Cost of services	49,497	49,134	99,015	98,476
Cost of goods sold
Operating expenses:
Cost of services	$ 15,874	$ 15,166	$ 30,511	$ 30,971