Recent Accounting Developments Recent Accounting Developments (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in cash flows from operating activities reclassified to investing activities	$ 150,816	$ 176,321
Increase in cash flows from investing activities reclassified from operating activities	$ (92,345)	(71,022)
Accounting Standards Update 2016-15 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in cash flows from operating activities reclassified to investing activities		(7,600)
Increase in cash flows from investing activities reclassified from operating activities		$ 7,600