Revenue Revenue (Details 2) $ in Thousands	Dec. 31, 2018 USD ($)
Period 1 [Member]
Revenue, Remaining Performance Obligation, Amount	$ 280,984
Period 2 [Member]
Revenue, Remaining Performance Obligation, Amount	227,981
Period 3 [Member]
Revenue, Remaining Performance Obligation, Amount	186,465
Period 4 [Member]
Revenue, Remaining Performance Obligation, Amount	169,252
Period 5 [Member]
Revenue, Remaining Performance Obligation, Amount	163,193
Thereafter [Member]
Revenue, Remaining Performance Obligation, Amount	$ 1,349,773