Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Increase decrease in stockholders equity roll forward
Total stockholders' equity	$ 2,396,505
Noncontrolling interest	124,043
Balance	2,520,548	$ 3,249,784
Net loss attributable to noncontrolling interest	(11,040)	(3,528)
Net income (loss)	13,829	(309,445)
Other comprehensive income	(1,434)	1,179
Dividends declared on preferred stocks	(171)	(171)
Dividends declared on common stock	(36,620)	(35,515)
Stock-based compensation	1,065	(121)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(316)
Excess tax benefit (net tax deficit) on stock-based compensation	(1,517)	(1,632)
Issuance of common stock		9,864
Contribution from noncontrolling interest		20,500
Total stockholders' equity	2,382,381	2,801,728
Noncontrolling interest	113,003	132,715
Balance	2,495,384	2,934,443
Total stockholders’ equity [Member]
Increase decrease in stockholders equity roll forward
Total stockholders' equity	2,396,505	3,134,041
Net income (loss) attributable to parent	24,869	(305,917)
Other comprehensive income	(1,434)	1,179
Dividends declared on preferred stocks	(171)	(171)
Dividends declared on common stock	(36,620)	(35,515)
Stock-based compensation	1,065	(121)
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	(316)
Excess tax benefit (net tax deficit) on stock-based compensation	(1,517)	(1,632)
Issuance of common stock		9,864
Contribution from noncontrolling interest		0
Total stockholders' equity	2,382,381	2,801,728
Noncontrolling interest [Member]
Increase decrease in stockholders equity roll forward
Noncontrolling interest	124,043	115,743
Net loss attributable to noncontrolling interest	(11,040)	(3,528)
Other comprehensive income	0	0
Dividends declared on preferred stocks	0	0
Dividends declared on common stock	0	0
Stock-based compensation	0	0
Issuance of common stock upon vesting of stock-based compensation, net of shares used for tax withholdings	0
Excess tax benefit (net tax deficit) on stock-based compensation	0	0
Issuance of common stock		0
Contribution from noncontrolling interest		20,500
Noncontrolling interest	$ 113,003	$ 132,715