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Commitments And Contingencies (Future Minimum Lease Payments) (Details)
ft² in Thousands
Sep. 30, 2017
USD ($)
ft²
Commitments and Contingencies Disclosure [Abstract]  
Boston lease per square foot annual increase $ 1
Boston Lease Square Feet | ft² 250
2017 $ 39,261,000
2018 30,988,000
2019 25,941,000
2020 28,134,000
2021 24,018,000
Thereafter 212,234,000
Total minimum lease payments 360,576,000
Boston lease annual increase $ 300,000