Other Assets - Equity Method Investee (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Assets [Abstract]
Current assets	$ 532,330	$ 492,707
Non-current assets	3,673,613	2,942,580
Total assets	4,205,943	3,435,287
Current liabilities	1,152,193	887,175
Non- current liabilities	1,974,166	1,704,495
Total liabilities	3,126,359	2,591,670
Noncontrolling interest	1,753	1,544
Total revenues	1,994,014	1,340,662	$ 990,172
Total expenses	(1,684,276)	(1,078,470)	(830,898)
Net income	$ 309,738	$ 262,192	$ 159,274