Leases (Summary of Lease Assets and Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease asset	$ 174,563	$ 0
Finance lease asset	18,502
Total lease assets	193,065
Operating lease liability, current	26,633
Finance lease liability, current	4,708
Total lease liabilities, current	31,341
Operating lease liability, noncurrent	204,336
Finance lease liability, noncurrent	20,348
Total lease liabilities, noncurrent	224,684
Total lease liabilities	$ 256,025