Condensed Financial Information of Registrant (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current assets:
Cash and cash equivalents	$ 795,770,000	$ 493,827,000	$ 455,886,000	$ 469,501,000
Investments	342,845,000	336,916,000
Income tax refundable	0	11,679,000
Deferred income taxes	32,443,000	18,327,000
Total current assets	1,349,126,000	1,048,082,000
Cash and cash equivalents	795,770,000	493,827,000	455,886,000	469,501,000
Investments	342,845,000	336,916,000
Property and equipment, net	221,443,000	190,934,000
Goodwill and indefinite-lived intangible assets	151,088,000	153,954,000
Total assets	1,934,822,000	1,652,146,000
Current liabilities:
Long-term Debt	175,468,000	169,526,000
Deferred income taxes	37,900,000	33,127,000
Other long-term liabilities	24,787,000	21,782,000
Total liabilities	1,152,508,000	897,073,000
Stockholders' equity:
Preferred stock, $0.001 par value; 20,000 shares authorized, no shares issued and outstanding
Accumulated other comprehensive loss	(457,000)	(1,405,000)
Treasury Stock, Value	(3,000,000)	0
Retained earnings	500,200,000	490,410,000
Total stockholders’ equity	782,314,000	755,073,000
Total liabilities and stockholders' equity	1,934,822,000	1,652,146,000
Parent Company [Member]
Current assets:
Cash and cash equivalents	39,068,000	14,650,000	57,020,000	26,040,000
Investments	2,015,000	2,010,000
Income tax refundable	8,868,000	14,126,000
Deferred income taxes	9,706,000	9,133,000
Due from affiliates	55,382,000	60,569,000
Prepaid and other current assets	19,164,000	10,467,000
Total current assets	134,203,000	110,955,000
Cash and cash equivalents	39,068,000	14,650,000	57,020,000	26,040,000
Investments	2,015,000	2,010,000
Property and equipment, net	108,808,000	82,437,000
Goodwill and indefinite-lived intangible assets	52,302,000	53,769,000
Auction rate securities	3,615,000	4,694,000
Investments in subsidiaries	768,765,000	740,345,000
Advances to related parties and other assets	34,600,000	32,473,000
Total assets	1,102,293,000	1,024,673,000
Current liabilities:
Accounts payable and accrued liabilities	73,883,000	71,392,000
Long-term Debt	215,468,000	169,526,000
Deferred income taxes	17,122,000	16,909,000
Other long-term liabilities	13,506,000	11,773,000
Total liabilities	319,979,000	269,600,000
Stockholders' equity:
Common stock, $0.001 par value; 80,000 shares authorized; outstanding: 46,762 shares at December 31, 2012 and 45,815 shares at December 31, 2011	47,000	46,000
Preferred stock, $0.001 par value; 20,000 shares authorized, no shares issued and outstanding	0	0
Paid-in capital	285,524,000	266,022,000
Accumulated other comprehensive loss	(457,000)	(1,405,000)
Treasury Stock, Value	(3,000,000)
Retained earnings	500,200,000	490,410,000
Total stockholders’ equity	782,314,000	755,073,000
Total liabilities and stockholders' equity	$ 1,102,293,000	$ 1,024,673,000