New Accounting Pronouncements Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 86,339	$ 67,562
Restricted cash held in escrow for like-kind exchange	146,110	116,405
Escrow Deposit	10,193	9,660
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 242,642	$ 193,627	$ 967,969	$ 57,038