Fair Value of Financial Assets and Liabilities, Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
Carrying Amount
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	[1]	$ 663,235	$ 663,069
Fair Value
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	[1]	$ 731,767	$ 730,284

[1] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmM0OTA5MGEyYmYzNTQ4MTM5YmQ3ZGRkZGU5NWFiODk3fFRleHRTZWxlY3Rpb246N0NEQTM3RkNBMDMxOUM0RjRERTgyRkQ2MUE4MzVBNEMM}