UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME [Abstract]
Operating revenues	$ 77,454	$ 71,378	$ 153,463	$ 140,201
Operating expenses:
Cost of goods and services, exclusive of depreciation and amortization shown separately below	30,528	29,969	61,229	58,998
Selling, general and administrative, exclusive of depreciation and amortization shown separately below	16,355	15,013	32,484	30,182
Depreciation and amortization	16,071	15,259	30,042	31,066
Total operating expenses	62,954	60,241	123,755	120,246
Operating income	14,500	11,137	29,708	19,955
Other income (expense):
Interest expense	(2,068)	(1,522)	(4,220)	(3,317)
Gain (loss) on investments, net	30	132	178	602
Non-operating income, net	458	259	979	447
Income from continuing operations before income taxes	12,920	10,006	26,645	17,687
Income tax expense	5,078	4,284	10,452	7,558
Net income from continuing operations	7,842	5,722	16,193	10,129
Losses from discontinued operations, net of tax benefit of $0, $106, $0 and $68, respectively	0	(162)	0	(103)
Net income	7,842	5,560	16,193	10,026
Other comprehensive income:
Unrealized gain on interest rate hedge, net of tax	2,775	0	3,307	0
Comprehensive income	$ 10,617	$ 5,560	$ 19,500	$ 10,026
Basic and diluted net income (loss) per share:
Net income from continuing operations (in dollars per share)	$ 0.33	$ 0.24	$ 0.67	$ 0.42
Losses from discontinued operations (in dollars per share)	$ 0	$ (0.01)	$ 0	$ 0
Net income (in dollars per share)	$ 0.33	$ 0.23	$ 0.67	$ 0.42
Weighted average shares outstanding, basic (in shares)	23,996	23,855	23,985	23,849
Weighted average shares, diluted (in shares)	24,078	23,892	24,055	23,880