Significant Accounting Policies and Recently Issued Accounting Pronouncement - Recently Issued Accounting Pronouncement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Dec. 31, 2015
Recently Issued Accounting Pronouncements
Cash flow from operations	$ 572,396	$ (883,412)	$ (938,325)
Cash and restricted cash at year end	155,924	38,173	99,642		$ 105,550
Future minimum lease payments	$ 93,700
Accounting Standards Update 2016-02: Leases | As adjusted
Recently Issued Accounting Pronouncements
right-of-use asset				$ 58,600
Lease liability				$ 79,300
ASU 2016-18 | Adjustment
Recently Issued Accounting Pronouncements
Cash flow from operations		173	197
Cash and restricted cash at year end		448	275
ASU 2016-18 | As previously reported
Recently Issued Accounting Pronouncements
Cash flow from operations		(883,585)	(938,522)
Cash and restricted cash at year end		$ 37,725	$ 99,367