Accounting Policies and Related Matters (Details 2) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies and Related Matters [Line Items]
Cash disbursed for acquisitions		$ (805,264)	$ (2,145,374)	$ (3,353,087)
Net cash provided from (used in) investing activities		154,581	(183,443)	(3,502,075)
Increase (decrease) in cash and cash equivalents		(297,917)	184,530	(130,733)
Cash and cash equivalents at beginning of period		419,378	422,690	553,423
Cash and cash equivalents at end of period		243,777	419,378	422,690
As Previously Reported
Accounting Policies and Related Matters [Line Items]
Cash disbursed for acquisitions			(2,145,590)	(3,364,891)
Decrease (increase) in restricted cash			(125,844)	29,719
Net cash provided from (used in) investing activities			(309,503)	(3,484,160)
Increase (decrease) in cash and cash equivalents	[1]		58,470	(112,818)
Cash and cash equivalents at beginning of period	[1]	419,378	360,908	473,726
Cash and cash equivalents at end of period	[1]		419,378	360,908
Accounting Standards Update 2016-18 [Member] | As Reported
Accounting Policies and Related Matters [Line Items]
Cash disbursed for acquisitions			(2,145,374)	(3,353,087)
Decrease (increase) in restricted cash			0	0
Net cash provided from (used in) investing activities			(183,443)	(3,502,075)
Increase (decrease) in cash and cash equivalents	[1]		184,530	(130,733)
Cash and cash equivalents at beginning of period		$ 607,220	422,690	553,423
Cash and cash equivalents at end of period			$ 607,220	$ 422,690

[1] Amounts in As Reported column include cash and cash equivalents and restricted cash as required. Amounts in the As Previously Reported column reflect only cash and cash equivalents.