Long-Term Debt (Details 6) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Maturities of outstanding debt
2015	$ 46,460,000
2016	16,364,000
2017	15,675,000
2018	15,601,000
2019	603,291,000
Thereafter	2,326,775,000
Total debt	3,024,166,000	2,107,589,000
Interest costs
Interest costs incurred	139,700,000	132,300,000	160,000,000
Interest costs incurred capitalized	2,500,000	4,600,000	1,400,000
Cash paid for interest	$ 114,300,000	$ 129,500,000	$ 154,100,000