CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Service Revenue
Service revenue	$ 485,175	$ 446,900	$ 404,234
Operating expenses:
Network operations (including $604, $573 and $584 of equity-based compensation expense, respectively), exclusive of amounts shown separately	209,278	194,066	174,510
Selling, general, and administrative (including $12,686, $10,162 and $10,931 of equity-based compensation expense, respectively)	127,915	120,709	113,103
Depreciation and amortization	75,926	75,235	70,527
Total operating expenses	413,119	390,010	358,140
Gains on equipment transactions	3,862	7,739	5,443
Gains on capital lease terminations			11,643
Losses on debt extinguishment and redemption		(587)	(10,144)
Operating income	75,918	64,042	53,036
Interest income and other	3,667	1,021	956
Interest expense	(48,467)	(40,803)	(41,280)
Income before income taxes	31,118	24,260	12,712
Income tax expense	(25,242)	(9,331)	(7,816)
Net income	5,876	14,929	4,896
Comprehensive income (loss):
Net income	5,876	14,929	4,896
Foreign currency translation adjustment	12,593	(2,500)	(8,231)
Comprehensive income (loss)	$ 18,469	$ 12,429	$ (3,335)
Net income per common share:
Basic net income per common share (in dollars per share)	$ 0.13	$ 0.33	$ 0.11
Diluted net income per common share (in dollars per share)	0.13	0.33	0.11
Dividends declared per common share (in dollars per share)	$ 1.80	$ 1.51	$ 1.46
Weighted-average common shares - basic (in shares)	44,855,263	44,641,805	44,888,723
Weighted-average common shares - diluted (in shares)	45,184,203	44,873,030	45,159,489