Consolidated Variable Interest Entities - Statements of Operations and Cash Flows (Details) - Variable Interest Entity, Primary Beneficiary - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Variable Interest Entity [Line Items]
Operating revenues	$ 203,426	$ 185,786
Operating expenses	59,525	49,623
Other expenses	1,913	384
Net income	141,988	135,779
Net cash provided by operating activities	160,769	115,644
Net cash used in investing activities	(81,687)	(123,522)
Net cash used in financing activities	$ (96,767)	$ (352,704)