Commitments and Contingencies (Summary of Future Lease Payments Under Non-Cancelable Capital and Operating Leases (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Capital
2018	$ 1,433
2019	1,094
2020	769
2021	597
2022	590
Thereafter	3,954
Total payments	8,437
Less amount representing interest	1,510
Present value of capitalized lease payments	6,927
Operating
2018	115,736
2019	91,226
2020	70,146
2021	47,356
2022	26,927
Thereafter	39,615
Total payments	391,006
Total Future Payments
2018	117,169
2019	92,320
2020	70,915
2021	47,953
2022	27,517
Thereafter	43,569
Total payments	$ 399,443