Basis of Presentation and Significant Accounting Policies, Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Recently Adopted Accounting Pronouncements
Proceeds from insurance settlements from net cash provided by operating activities	$ 2,278	$ 647
Cash and cash equivalents at beginning of period	104,374
Cash, cash equivalents and restricted cash at beginning of period	243,772	167,960
Net increase in cash, cash equivalents and restricted cash	(9,565)	52,146
Cash and cash equivalents at end of period	102,548
Cash, cash equivalents and restricted cash at end of period	234,207	220,106
Net cash provided by operating activities: change in operating assets and liabilities	(18,961)	(42,967)
Net cash (used in) provided by investing activities	(158,974)	45,003
Net cash provided by (used in) financing activities	128,612	(65,430)
Reclassification of net unrealized gains on available-for-sale securities into accumulated deficit		29
Accumulated deficit	(88,528)		$ (101,926)
ASU 2016-15
Recently Adopted Accounting Pronouncements
Proceeds from insurance settlements from net cash provided by operating activities		600
Net cash (used in) provided by investing activities		(600)
Previously reported under GAAP
Recently Adopted Accounting Pronouncements
Cash and cash equivalents at beginning of period		138,645
Net decrease in cash and cash equivalents		(33,802)
Cash and cash equivalents at end of period		104,843
Net cash provided by operating activities: change in operating assets and liabilities		(42,461)
Net cash (used in) provided by investing activities		44,356
Net cash provided by (used in) financing activities		(151,398)
ASU 2016-18 and ASU 2016-15
Recently Adopted Accounting Pronouncements
Cash, cash equivalents and restricted cash at beginning of period		167,960
Net increase in cash, cash equivalents and restricted cash		52,146
Cash, cash equivalents and restricted cash at end of period		220,106
Net cash provided by operating activities: change in operating assets and liabilities		(42,967)
Net cash (used in) provided by investing activities		45,003
Net cash provided by (used in) financing activities		$ (65,430)
ASU 2016-01
Recently Adopted Accounting Pronouncements
Reclassification of net unrealized gains on available-for-sale securities into accumulated deficit	(200)
Accumulated deficit	$ 200