Segment Reporting - Selected Financial Data for Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
External 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
Wireless
External revenue
Operating revenues	112,870	113,509	227,254	225,074
Cable
External revenue
Operating revenues	33,209	31,014	65,449	61,694
Wireline
External revenue
Operating revenues	12,835	11,978	25,054	23,871
Other
External revenue
Operating revenues	0	0	0	0
Intersegment Eliminations
External revenue
Operating revenues	(9,443)	(9,475)	(18,872)	(19,559)
Operating expenses:
Selling, general and administrative	(698)	(611)	(1,368)	(1,329)
Depreciation and amortization	0	0	0	0
Total operating expenses	(9,443)	(9,475)	(18,872)	(19,559)
Operating income	0	0	0	0
Intersegment Eliminations | Wireless
External revenue
Operating revenues	(1,270)	(1,244)	(2,540)	(2,483)
Intersegment Eliminations | Cable
External revenue
Operating revenues	(1,481)	(1,097)	(2,950)	(2,128)
Intersegment Eliminations | Wireline
External revenue
Operating revenues	(6,692)	(7,134)	(13,382)	(14,948)
Intersegment Eliminations | Other
External revenue
Operating revenues	0	0	0	0
Operating Segments | Wireless
External revenue
Operating revenues	114,140	114,753	229,794	227,557
Operating expenses:
Selling, general and administrative	10,592	12,367	21,954	24,502
Depreciation and amortization	32,219	31,565	63,269	65,490
Total operating expenses	92,116	92,502	182,433	188,039
Operating income	22,024	22,251	47,361	39,518
Operating Segments | Cable
External revenue
Operating revenues	34,690	32,111	68,399	63,822
Operating expenses:
Selling, general and administrative	5,536	4,661	11,262	9,609
Depreciation and amortization	6,555	6,179	13,013	12,203
Total operating expenses	27,904	26,028	55,910	52,212
Operating income	6,786	6,083	12,489	11,610
Operating Segments | Wireline
External revenue
Operating revenues	19,527	19,112	38,436	38,819
Operating expenses:
Selling, general and administrative	1,988	1,686	3,831	3,403
Depreciation and amortization	3,447	3,240	6,980	6,634
Total operating expenses	14,433	14,319	28,996	29,254
Operating income	5,094	4,793	9,440	9,565
Operating Segments | Other
External revenue
Operating revenues	0	0	0	0
Operating expenses:
Selling, general and administrative	9,752	11,812	20,213	22,480
Depreciation and amortization	132	133	270	277
Total operating expenses	9,884	11,958	20,483	22,770
Operating income	(9,884)	(11,958)	(20,483)	(22,770)
Service revenue
External revenue
Operating revenues	130,624	129,739	262,889	255,683
Service revenue | Wireless
External revenue
Operating revenues	94,350	95,690	191,425	187,855
Service revenue | Cable
External revenue
Operating revenues	30,716	28,748	60,421	57,219
Service revenue | Wireline
External revenue
Operating revenues	5,558	5,301	11,043	10,609
Service revenue | Other
External revenue
Operating revenues	0	0	0	0
Equipment revenue
External revenue
Operating revenues	16,855	16,009	32,467	33,588
Equipment revenue | Wireless
External revenue
Operating revenues	16,548	15,819	31,839	33,193
Equipment revenue | Cable
External revenue
Operating revenues	255	144	525	303
Equipment revenue | Wireline
External revenue
Operating revenues	52	46	103	92
Equipment revenue | Other
External revenue
Operating revenues	0	0	0	0
Tower revenue
External revenue
Operating revenues	1,654	1,636	3,325	3,294
Tower revenue | Wireless
External revenue
Operating revenues	1,654	1,636	3,325	3,294
Tower revenue | Cable
External revenue
Operating revenues	0	0	0
Tower revenue | Wireline
External revenue
Operating revenues	0	0	0
Tower revenue | Other
External revenue
Operating revenues	0	0	0
Other revenue
External revenue
Operating revenues	9,781	9,117	19,076	18,074
Other revenue | Wireless
External revenue
Operating revenues	318	364	665	732
Other revenue | Cable
External revenue
Operating revenues	2,238	2,122	4,503	4,172
Other revenue | Wireline
External revenue
Operating revenues	7,225	6,631	13,908	13,170
Other revenue | Other
External revenue
Operating revenues	0	0	0	0
Cost of services
Operating expenses:
Cost of services	49,497	49,134	99,015	98,476
Cost of services | Intersegment Eliminations
Operating expenses:
Cost of services	(8,746)	(8,864)	(17,504)	(18,230)
Cost of services | Operating Segments | Wireless
Operating expenses:
Cost of services	33,563	33,488	67,041	67,238
Cost of services | Operating Segments | Cable
Operating expenses:
Cost of services	15,701	15,125	31,348	30,281
Cost of services | Operating Segments | Wireline
Operating expenses:
Cost of services	8,979	9,373	18,130	19,175
Cost of services | Operating Segments | Other
Operating expenses:
Cost of services	0	12	0	12
Cost of goods sold
Operating expenses:
Cost of services	15,874	15,166	30,511	30,971
Cost of goods sold | Intersegment Eliminations
Operating expenses:
Cost of services	1	0	0	0
Cost of goods sold | Operating Segments | Wireless
Operating expenses:
Cost of services	15,742	15,082	30,169	30,809
Cost of goods sold | Operating Segments | Cable
Operating expenses:
Cost of services	112	63	287	119
Cost of goods sold | Operating Segments | Wireline
Operating expenses:
Cost of services	19	20	55	42
Cost of goods sold | Operating Segments | Other
Operating expenses:
Cost of services	$ 0	$ 1	$ 0	$ 1