Segment Reporting - Selected Financial Data for Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
External revenue
Operating revenues	$ 158,843	$ 154,138
Operating expenses:
Selling, general and administrative	28,722	28,750
Depreciation and amortization	41,179	43,487
Total operating expenses	134,056	137,384
Operating income (loss)	24,787	16,754
Wireless
External revenue
Operating revenues	114,384	111,565
Cable
External revenue
Operating revenues	32,240	30,680
Wireline
External revenue
Operating revenues	12,219	11,893
Other
External revenue
Operating revenues	0	0
Intersegment Eliminations
External revenue
Operating revenues	(9,429)	(10,084)
Operating expenses:
Selling, general and administrative	(670)	(718)
Depreciation and amortization	0	0
Total operating expenses	(9,429)	(10,084)
Operating income (loss)	0	0
Intersegment Eliminations | Wireless
External revenue
Operating revenues	(1,270)	(1,239)
Intersegment Eliminations | Cable
External revenue
Operating revenues	(1,469)	(1,031)
Intersegment Eliminations | Wireline
External revenue
Operating revenues	(6,690)	(7,814)
Intersegment Eliminations | Other
External revenue
Operating revenues	0	0
Operating Segments
External revenue
Operating revenues	168,272	164,222
Operating Segments | Wireless
External revenue
Operating revenues	115,654	112,804
Operating expenses:
Selling, general and administrative	11,362	12,135
Depreciation and amortization	31,050	33,925
Total operating expenses	90,317	95,537
Operating income (loss)	25,337	17,267
Operating Segments | Cable
External revenue
Operating revenues	33,709	31,711
Operating expenses:
Selling, general and administrative	5,726	4,948
Depreciation and amortization	6,458	6,024
Total operating expenses	28,006	26,184
Operating income (loss)	5,703	5,527
Operating Segments | Wireline
External revenue
Operating revenues	18,909	19,707
Operating expenses:
Selling, general and administrative	1,843	1,717
Depreciation and amortization	3,533	3,394
Total operating expenses	14,563	14,935
Operating income (loss)	4,346	4,772
Operating Segments | Other
External revenue
Operating revenues	0	0
Operating expenses:
Selling, general and administrative	10,461	10,668
Depreciation and amortization	138	144
Total operating expenses	10,599	10,812
Operating income (loss)	(10,599)	(10,812)
Service revenue
External revenue
Operating revenues	132,265	125,944
Service revenue | Wireless
External revenue
Operating revenues	97,075	92,165
Service revenue | Cable
External revenue
Operating revenues	29,705	28,471
Service revenue | Wireline
External revenue
Operating revenues	5,485	5,308
Service revenue | Other
External revenue
Operating revenues	0	0
Equipment revenue
External revenue
Operating revenues	15,612	17,579
Equipment revenue | Wireless
External revenue
Operating revenues	15,291	17,374
Equipment revenue | Cable
External revenue
Operating revenues	270	159
Equipment revenue | Wireline
External revenue
Operating revenues	51	46
Equipment revenue | Other
External revenue
Operating revenues	0	0
Other
External revenue
Operating revenues	10,966	10,615
Other | Wireless
External revenue
Operating revenues	2,018	2,026
Other | Cable
External revenue
Operating revenues	2,265	2,050
Other | Wireline
External revenue
Operating revenues	6,683	6,539
Other | Other
External revenue
Operating revenues	0	0
Cost of services
Operating expenses:
Cost of services	49,518	49,342
Cost of services | Intersegment Eliminations
Operating expenses:
Cost of services	(8,758)	(9,366)
Cost of services | Operating Segments | Wireless
Operating expenses:
Cost of services	33,478	33,750
Cost of services | Operating Segments | Cable
Operating expenses:
Cost of services	15,647	15,156
Cost of services | Operating Segments | Wireline
Operating expenses:
Cost of services	9,151	9,802
Cost of services | Operating Segments | Other
Operating expenses:
Cost of services	0	0
Cost of goods sold
Operating expenses:
Cost of services	14,637	15,805
Cost of goods sold | Intersegment Eliminations
Operating expenses:
Cost of services	(1)	0
Cost of goods sold | Operating Segments | Wireless
Operating expenses:
Cost of services	14,427	15,727
Cost of goods sold | Operating Segments | Cable
Operating expenses:
Cost of services	175	56
Cost of goods sold | Operating Segments | Wireline
Operating expenses:
Cost of services	36	22
Cost of goods sold | Operating Segments | Other
Operating expenses:
Cost of services	$ 0	$ 0