Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended										12 Months Ended
	Dec. 31, 2017	[1]	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	[2]	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Computation of basic and diluted earnings per share
Numerator for basic and diluted earnings per share - net income attributable to common stockholders	$ (111,523)		$ 74,043	$ 188,429	$ 312,639	$ 333,044	$ 334,910		$ 195,474	$ 148,969	$ 463,595	$ 1,012,397	$ 818,344
Denominator for basic earnings per share: weighted-average shares											367,237	358,275	348,240
Effect of dilutive securities:
Employee stock options											47	110	143
Non-vested restricted shares											482	449	535
Redeemable shares											1,235	1,393	310
Convertible senior unsecured notes											0	0	196
Dilutive potential common shares											1,764	1,952	1,184
Diluted											369,001	360,227	349,424
Net income attributable to common stockholders	$ (0.31)		$ 0.2	$ 0.51	$ 0.86	$ 0.92	$ 0.93		$ 0.55	$ 0.42	$ 1.26	$ 2.83	$ 2.35
Net income attributable to common stockholders	$ (0.31)		$ 0.2	$ 0.51	$ 0.86	$ 0.91	$ 0.93		$ 0.54	$ 0.42	$ 1.26	$ 2.81	$ 2.34

[1] The decrease in net income (loss) and amounts per share are primarily attributable to $99,821,100 impairment of assets and $62,966,000 provision for loan losses recognized in the fourth quarter as compared to none in the third quarter.

[2] The increase in net income and amounts per share are primarily attributable to gains on sales of real estate of $162,351,000 for the third quarter as compared to gains of $1,530,000 for the second quarter.