Basis of Presentation (Reconciliation of Weighted Average Shares Table) (Details) - USD ($) shares in Thousands, $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator
Net income - basic		$ 146,692	$ (25,674)	$ 30,222	$ 39,578	$ 121,018	$ 69,800
Interest on convertible senior notes including amortization of discount, net of tax		548		130		548	539
Net income - diluted		$ 147,240		$ 30,352		$ 121,566	$ 70,339
Denominator
Weighted average common shares outstanding - basic		452,612		433,467		452,169	413,217
Restricted stock and performance-based equity awards		2,835		8,586		3,301	6,877
Convertible senior notes	[1]	11,980		15,112		5,990	34,372
Weighted average common shares outstanding - diluted		467,427		457,165		461,460	454,466

[1] (1) For the three and six months ended June 30, 2019, shares shown under “convertible senior notes” represent the prorated portion of the approximately 90.9 million shares of the Company’s common stock issuable upon full conversion of our convertible senior notes (see Note 4, Long-Term Debt – 2019 Note Exchanges).