Supplemental Cash Flow Information of the Company - Reconciliation of cash and cash equivalents and restricted cash (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents at beginning of period	$ 193,418	$ 26,332	$ 56,508
Restricted cash at beginning of period	56,711	266,158	696
Cash and cash equivalents and restricted cash, beginning of period	250,129	292,490	57,204
Cash and cash equivalents at end of period	387,616	193,418	26,332
Restricted cash at end of period	8,249	56,711	266,158
Cash and cash equivalents and restricted cash, end of period	$ 395,865	$ 250,129	$ 292,490