UNAUDITED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (LOSS) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
UNAUDITED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (LOSS) [Abstract]
Operating revenues	$ 84,287	$ 80,452
Operating expenses:
Cost of goods and services, exclusive of depreciation and amortization shown separately below	30,691	32,236
Selling, general and administrative, exclusive of depreciation and amortization shown separately below	18,733	17,149
Depreciation and amortization	16,337	15,387
Total operating expenses	65,761	64,772
Operating income	18,526	15,680
Other income (expense):
Interest expense	(1,915)	(2,048)
Gain (loss) on investments, net	102	(18)
Non-operating income, net	432	628
Income before income taxes	17,145	14,242
Income tax expense	6,859	5,626
Net income	10,286	8,616
Other comprehensive income:
Unrealized gain (loss) on interest rate hedge, net of tax	(907)	(347)
Comprehensive Income	$ 9,379	$ 8,269
Earnings per share:
Basic (in dollars per share)	$ 0.43	$ 0.36
Diluted (in dollars per share)	$ 0.42	$ 0.36
Weighted average shares outstanding, basic (in shares)	24,153	24,059
Weighted average shares outstanding, diluted (in shares)	24,451	24,221