Consolidated Variable Interest Entities (Statements of Operations and Cash Flows) (Details) - Variable Interest Entity, Primary Beneficiary - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Variable Interest Entity [Line Items]
Operating revenues	$ 172,004	$ 144,613	$ 352,605	$ 299,424
Operating expenses	(48,483)	(44,255)	(97,855)	(86,314)
Other income (expenses)	469	(15,513)	(2,651)	(46,590)
Net income	123,990	84,845	252,099	166,520
Net cash provided by operating activities	149,855	124,443	267,426	239,102
Net cash used in investing activities	(200,284)	(233,448)	(303,958)	(765,883)
Net cash provided by (used in) financing activities	$ 134,410	$ (101,601)	$ (229,927)	$ 356,500