CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Service revenue	$ 589,797	$ 568,103	$ 546,159
Operating expenses:
Network operations (including $2,521, $1,219 and $994 of equity-based compensation expense, respectively), exclusive of amounts shown separately	226,337	219,157	219,801
Selling, general, and administrative (including $24,301, $22,306 and $17,466 of equity-based compensation expense, respectively)	162,380	158,476	146,913
Depreciation and amortization	89,240	83,477	80,247
Total operating expenses	477,957	461,110	446,961
Losses on lease terminations	7,400
Gains on equipment transactions	18	352	1,059
Gains (losses) on lease terminations	7,375	(423)
Operating income	119,233	106,922	100,257
Interest expense	(67,074)	(62,486)	(57,453)
Realized foreign exchange gain on 2024 Euro Notes		2,533
Unrealized foreign exchange gain (loss) on 2024 Euro Notes	32,522	(36,997)	2,271
Interest income and other	1,437	978	7,599
Income before income taxes	71,420	10,312	52,674
Income tax expense	(23,235)	(4,096)	(15,154)
Net income	48,185	6,216	37,520
Comprehensive income:
Net income	48,185	6,216	37,520
Foreign currency translation adjustment	(9,697)	11,020	(1,398)
Comprehensive income	$ 38,488	$ 17,236	$ 36,122
Net income (loss) per common share:
Basic net income per common share	$ 1.04	$ 0.14	$ 0.82
Diluted net income per common share	1.03	0.13	0.81
Dividends declared per common share	$ 3.17	$ 2.78	$ 2.44
Weighted-average common shares - basic (in shares)	46,419,180	45,947,772	45,542,315
Weighted-average common shares - diluted (in shares)	46,963,920	46,668,198	46,080,395
Senior notes
Operating expenses:
Loss on debt extinguishment and redemption - 2021 Notes		$ (638)
2022 Notes
Operating expenses:
Loss on debt extinguishment and redemption - 2021 Notes	$ (14,698)
Loss on debt extinguishment and redemption - 2022 Notes	$ (14,698)