UNAUDITED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
UNAUDITED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (LOSS) [Abstract]
Operating revenues	$ 85,212	$ 82,268	$ 255,202	$ 244,136
Operating expenses:
Cost of goods and services, exclusive of depreciation and amortization shown separately below	30,570	33,330	91,541	97,970
Selling, general and administrative, exclusive of depreciation and amortization shown separately below	20,435	18,063	58,177	51,836
Depreciation and amortization	19,118	16,731	53,119	48,714
Total operating expenses	70,123	68,124	202,837	198,520
Operating income	15,089	14,144	52,365	45,616
Other income (expense):
Interest expense	(1,808)	(2,007)	(5,663)	(6,119)
Gain (loss) on investments, net	(211)	239	(12)	335
Non-operating income, net	391	409	1,265	1,496
Income before income taxes	13,461	12,785	47,955	41,328
Income tax expense	5,465	4,782	19,199	16,094
Net income	7,996	8,003	28,756	25,234
Other comprehensive income:
Unrealized gain (loss) on interest rate hedge, net of tax	(979)	476	(1,560)	(784)
Comprehensive income	$ 7,017	$ 8,479	$ 27,196	$ 24,450
Earnings per share:
Basic (in dollars per share)	$ 0.33	$ 0.33	$ 1.19	$ 1.05
Diluted (in dollars per share)	$ 0.33	$ 0.33	$ 1.17	$ 1.04
Weighted average shares outstanding, basic (in shares)	24,203	24,113	24,182	24,091
Weighted average shares outstanding, diluted (in shares)	24,535	24,393	24,483	24,334