Long-term Debt Principal Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 46,063
Long-term Debt, Maturities, Repayments of Principal in Year Two	145,396
Long-term Debt, Maturities, Repayments of Principal in Year Three	51,117
Long-term Debt, Maturities, Repayments of Principal in Year Four	29,273
Long-term Debt, Maturities, Repayments of Principal in Year Five	798,459
Long-term Debt, Maturities, Repayments of Principal after Year Five	1,412,264
Long-term Debt, Gross	2,482,572
Debt Instrument, Unamortized Discount and Debt Issue Costs	60,271
Long-term Debt	$ 2,422,301	$ 2,155,197