Interim Consolidated Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interim Consolidated Financial Information (Unaudited)
Revenues	$ 444,156	$ 381,534	$ 326,444	$ 384,082	$ 326,498	$ 269,469	$ 246,288	$ 263,464	$ 1,536,216	$ 1,105,719	$ 753,751
Net income (loss)	$ (149,629)	$ 36,054	$ (12,484)	$ (187,083)	$ 8,873	$ 36,877	$ 34,425	$ 24,047	$ (313,142)	$ 104,222	$ 6,531
Basic net income (loss) per share	$ (0.71)	$ 0.17	$ (0.06)	$ (0.96)	$ 0.05	$ 0.20	$ 0.18	$ 0.13	$ (1.53)	$ 0.55	$ 0.04
Diluted net income (loss) per share	$ (0.71)	$ 0.17	$ (0.06)	$ (0.96)	$ 0.05	$ 0.19	$ 0.18	$ 0.12	$ (1.53)	$ 0.54	$ 0.03
Shares used in computation of basic net income (loss) per share	211,125,000	206,796,000	205,141,000	195,260,000	188,598,000	188,029,000	187,682,000	187,184,000	204,580,000	187,873,000	179,601,000
Shares used in computation of diluted net income (loss) per share	211,125,000	212,610,000	205,141,000	195,260,000	195,187,000	194,265,000	193,015,000	192,625,000	204,580,000	194,125,000	187,302,000