Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Numerator for basic and diluted earnings per share - net income (loss) attributable to common stockholders	$ 137,762	$ 154,432	$ 418,232	$ 592,103
Denominator for basic earnings per share - weighted average shares (in shares)	404,607,000	371,640,000	398,073,000	371,552,000
Effect of dilutive securities:
Employee stock options (in shares)	0	14,000	1,000	15,000
Non-vested restricted shares (in shares)	955,000	325,000	911,000	523,000
Redeemable shares (in shares)	1,096,000	1,096,000	1,096,000	1,096,000
Employee stock purchase program (in shares)	15,000	0	15,000	0
Dilutive potential common shares (in shares)	2,066,000	1,435,000	2,023,000	1,634,000
Denominator for diluted earnings per share - adjusted weighted average shares (in shares)	406,673,000	373,075,000	400,096,000	373,186,000
Basic earnings per share (in USD per share)	$ 0.34	$ 0.42	$ 1.05	$ 1.59
Diluted earnings per share (in USD per share)	$ 0.34	$ 0.41	$ 1.05	$ 1.59
Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of shares not included in the computation of diluted earnings per share because such options were anti-dilutive (in shares)			2,194,575