Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Computation of basic and diluted earnings per share
Numerator for basic and diluted earnings per share - net income attributable to common stockholders	$ 224,324	$ 589,876	$ 137,762	$ 280,470	$ 101,763	$ 64,384	$ 154,432	$ 437,671	$ 1,232,432	$ 758,250	$ 463,595
Denominator for basic earnings per share - weighted average shares (in shares)									401,845,000	373,620,000	367,237,000
Effect of dilutive securities:
Employee stock options (in shares)									0	9,000	47,000
Non-vested restricted shares (in shares)									835,000	512,000	482,000
Redeemable shares (in shares)									1,112,000	1,096,000	1,235,000
Employee stock purchase program (in shares)									16,000	13,000	0
Dilutive potential common shares (in shares)									1,963,000	1,630,000	1,764,000
Denominator for diluted earnings per share - adjusted weighted average shares (in shares)									403,808,000	375,250,000	369,001,000
Basic earnings per share (in USD per share)	$ 0.55	$ 1.46	$ 0.34	$ 0.72	$ 0.27	$ 0.17	$ 0.42	$ 1.18	$ 3.07	$ 2.03	$ 1.26
Diluted earnings per share (in USD per share)	$ 0.55	$ 1.45	$ 0.34	$ 0.71	$ 0.27	$ 0.17	$ 0.41	$ 1.17	$ 3.05	$ 2.02	$ 1.26
Stock Option
Effect of dilutive securities:
Number of shares not included in the computation of diluted earnings per share because such options were anti-dilutive									4,935,804