Leases (Summary of Lease Assets and Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease asset	$ 175,677	$ 0
Finance lease asset	17,240
Total lease assets	192,917
Operating lease liability, current	27,056
Finance lease liability, current	4,389
Total lease liabilities, current	31,445
Operating lease liability, noncurrent	203,815
Finance lease liability, noncurrent	19,520
Total lease liabilities, noncurrent	223,335
Total lease liabilities	$ 254,780