Borrowing Arrangements - Maturities (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Debt Disclosure [Abstract]
2018	$ 47,300
2019	241,158
2020	158,547
2021	248,414
2022	168,625
Thereafter	1,356,449
Net unamortized premiums	3,253
Unamortized deferred financing costs	(23,729)
Long-term Debt	$ 2,200,017