New Accounting Pronouncements Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 160,861	$ 67,562
Restricted cash held in escrow for like-kind exchange	59,196	116,405
Escrow Deposit	8,306	9,660
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 228,363	$ 193,627	$ 79,577	$ 57,038