Guarantor/Non-Guarantor Condensed Consolidated Financial Statements (Balance Sheet (Unaudited)) (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 23,711,000	$ 27,385,000	$ 17,576,000	$ 23,733,000
Receivables, net of allowance	200,537,000	176,360,000
Intercompany receivable (payable)	0	0
Deferred income taxes	32,365,000	13,092,000
Inventory	13,466,000	13,232,000
Prepaid expenses and other current assets	9,390,000	9,311,000
Total current assets	279,469,000	239,380,000
Net property and equipment	923,440,000	937,657,000
Investments in subsidiaries	0	0
Intangible assets, net of accumulated amortization	28,276,000	32,269,000
Goodwill			0		41,700,000
Noncurrent deferred income taxes	4,010,000	1,156,000
Other long-term assets	16,236,000	19,161,000
Total assets	1,251,431,000	1,229,623,000	1,291,533,000
Current liabilities:
Accounts payable	54,735,000	43,718,000
Current portion of long-term debt	429,000	2,847,000
Deferred revenues	3,306,000	699,000
Accrued expenses	71,783,000	73,569,000
Total current liabilities	130,253,000	120,833,000
Long-term debt, less current portion	493,630,000	499,666,000
Noncurrent deferred income taxes	102,988,000	84,636,000
Other long-term liabilities	4,771,000	6,055,000
Total liabilities	731,642,000	711,190,000
Total shareholders' equity	519,789,000	518,433,000
Total liabilities and shareholders' equity	1,251,431,000	1,229,623,000
Parent [Member]
Current assets:
Cash and cash equivalents	22,010,000	28,368,000	12,491,000	18,479,000
Receivables, net of allowance	1,203,000	905,000
Intercompany receivable (payable)	(24,837,000)	(24,837,000)
Deferred income taxes	22,710,000	1,143,000
Inventory	0	0
Prepaid expenses and other current assets	1,592,000	1,013,000
Total current assets	22,678,000	6,592,000
Net property and equipment	4,351,000	4,531,000
Investments in subsidiaries	913,402,000	939,091,000
Intangible assets, net of accumulated amortization	76,000	75,000
Noncurrent deferred income taxes	77,957,000	78,486,000
Other long-term assets	9,230,000	7,513,000
Total assets	1,027,694,000	1,036,288,000
Current liabilities:
Accounts payable	1,447,000	757,000
Current portion of long-term debt	0	0
Deferred revenues	0	0
Accrued expenses	11,825,000	16,368,000
Total current liabilities	13,272,000	17,125,000
Long-term debt, less current portion	493,564,000	499,586,000
Noncurrent deferred income taxes	0	0
Other long-term liabilities	319,000	394,000
Total liabilities	507,155,000	517,105,000
Total shareholders' equity	520,539,000	519,183,000
Total liabilities and shareholders' equity	1,027,694,000	1,036,288,000
Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	(1,485,000)	(2,059,000)	(1,771,000)	(5,401,000)
Receivables, net of allowance	146,019,000	125,979,000
Intercompany receivable (payable)	52,296,000	52,671,000
Deferred income taxes	8,122,000	8,005,000
Inventory	7,423,000	7,415,000
Prepaid expenses and other current assets	5,364,000	7,094,000
Total current assets	217,739,000	199,105,000
Net property and equipment	828,830,000	846,632,000
Investments in subsidiaries	124,684,000	120,630,000
Intangible assets, net of accumulated amortization	28,200,000	32,194,000
Noncurrent deferred income taxes	0	0
Other long-term assets	1,722,000	2,009,000
Total assets	1,201,175,000	1,200,570,000
Current liabilities:
Accounts payable	47,929,000	37,797,000
Current portion of long-term debt	429,000	2,847,000
Deferred revenues	1,563,000	699,000
Accrued expenses	52,891,000	51,739,000
Total current liabilities	102,812,000	93,082,000
Long-term debt, less current portion	66,000	80,000
Noncurrent deferred income taxes	180,945,000	163,122,000
Other long-term liabilities	3,950,000	5,195,000
Total liabilities	287,773,000	261,479,000
Total shareholders' equity	913,402,000	939,091,000
Total liabilities and shareholders' equity	1,201,175,000	1,200,570,000
Non-Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	3,186,000	1,076,000	6,856,000	10,655,000
Receivables, net of allowance	54,424,000	49,476,000
Intercompany receivable (payable)	(27,459,000)	(27,834,000)
Deferred income taxes	1,533,000	3,944,000
Inventory	6,043,000	5,817,000
Prepaid expenses and other current assets	2,434,000	1,204,000
Total current assets	40,161,000	33,683,000
Net property and equipment	91,009,000	87,244,000
Investments in subsidiaries	0	0
Intangible assets, net of accumulated amortization	0	0
Noncurrent deferred income taxes	4,010,000	1,156,000
Other long-term assets	5,284,000	9,639,000
Total assets	140,464,000	131,722,000
Current liabilities:
Accounts payable	5,359,000	5,164,000
Current portion of long-term debt	0	0
Deferred revenues	1,743,000	0
Accrued expenses	8,176,000	5,462,000
Total current liabilities	15,278,000	10,626,000
Long-term debt, less current portion	0	0
Noncurrent deferred income taxes	0	0
Other long-term liabilities	502,000	466,000
Total liabilities	15,780,000	11,092,000
Total shareholders' equity	124,684,000	120,630,000
Total liabilities and shareholders' equity	140,464,000	131,722,000
Eliminations [Member]
Current assets:
Cash and cash equivalents	0	0
Receivables, net of allowance	(1,109,000)	0
Intercompany receivable (payable)	0	0
Deferred income taxes	0	0
Inventory	0	0
Prepaid expenses and other current assets	0	0
Total current assets	(1,109,000)	0
Net property and equipment	(750,000)	(750,000)
Investments in subsidiaries	(1,038,086,000)	(1,059,721,000)
Intangible assets, net of accumulated amortization	0	0
Noncurrent deferred income taxes	(77,957,000)	(78,486,000)
Other long-term assets	0	0
Total assets	(1,117,902,000)	(1,138,957,000)
Current liabilities:
Accounts payable	0	0
Current portion of long-term debt	0	0
Deferred revenues	0	0
Accrued expenses	(1,109,000)	0
Total current liabilities	(1,109,000)	0
Long-term debt, less current portion	0	0
Noncurrent deferred income taxes	(77,957,000)	(78,486,000)
Other long-term liabilities	0	0
Total liabilities	(79,066,000)	(78,486,000)
Total shareholders' equity	(1,038,836,000)	(1,060,471,000)
Total liabilities and shareholders' equity	$ (1,117,902,000)	$ (1,138,957,000)