Fair Value of Financial Instruments (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Inputs, Level 1 [Member]
Financial Assets:
Cash and cash equivalents	$ 154,552	$ 259,266
Restricted cash	0	0
Total Financial Assets	176,550	280,150
Financial Liabilities:
Total debt	0	0
Total Financial Liabilities	0	0
Fair Value, Inputs, Level 2 [Member]
Financial Assets:
Cash and cash equivalents	0	0
Restricted cash	22,081	22,044
Total Financial Assets	22,081	22,044
Financial Liabilities:
Total debt	881,011	828,990
Total Financial Liabilities	881,011	828,990
Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Assets:
Cash and cash equivalents	154,552	259,266
Restricted cash	22,081	22,044
Total Financial Assets	198,631	302,194
Financial Liabilities:
Total debt	881,011	828,990
Total Financial Liabilities	881,011	828,990
Interest Rate Swap [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Liabilities:
Interest rate swap agreements	0	0
Interest Rate Swap [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Liabilities:
Interest rate swap agreements	7,136	5,078
Interest Rate Swap [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Liabilities:
Interest rate swap agreements	7,136	5,078
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets:
Equity securities	21,998	20,884
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets:
Equity securities	0	0
Equity Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Assets:
Equity securities	$ 21,998	$ 20,884