Significant Accounting Policies Leases (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Mar. 31, 2018
Operating Lease, Liability	$ 168,100
Retained earnings	$ 2,031,487		$ 1,997,785	$ 1,853,351
Change Due To Adoption of ASC 842
Assets, Noncurrent		$ 160,800
Operating Lease, Liability		161,400
Retained earnings		$ (600)