Consolidated Statement of Changes in Partner Capital Statement - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Dividends, Preferred Stock, Cash		$ 3,241
Shareholders' Equity		6,764,502
Net income	$ 53,465	(20,715)
Other comprehensive income (loss)	11,524	2,620
Deferred Compensation Plan	(3)
Partners' Capital Account, Contributions		153
Partners' Capital Account, Distributions	96,419	54,317
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company	(124,989)
Common unit issued as a result of common stock issued by Parent Company, net of purchases	(6,275)
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	4,121	3,733
Stockholders Equity including noncontrolling interest	6,605,381
Common unit redeemed as result of common stock redeemed by parent		4,461,767
Noncontrolling Interest [Member]
Dividends, Preferred Stock, Cash		0
Shareholders' Equity	30,233	35,217
Net income	694	671
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest	460	63
Deferred Compensation Plan	0
Partners' Capital Account, Contributions		153
Partners' Capital Account, Distributions	1,018	838
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company	0
Common unit issued as a result of common stock issued by Parent Company, net of purchases	0
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	0	0
Common unit redeemed as result of common stock redeemed by parent		0
Partners Capital Total [Member]
Dividends, Preferred Stock, Cash		3,241
Shareholders' Equity	6,575,148	6,729,285
Net income	52,771	(21,386)
Other comprehensive income (loss)	11,064	2,557
Deferred Compensation Plan	(3)
Partners' Capital Account, Contributions		0
Partners' Capital Account, Distributions	95,401	53,479
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company	(124,989)
Common unit issued as a result of common stock issued by Parent Company, net of purchases	(6,275)
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	4,121	3,733
Common unit redeemed as result of common stock redeemed by parent		4,461,767
AOCI Attributable to Parent [Member]
Dividends, Preferred Stock, Cash		0
Shareholders' Equity	4,764	(15,791)
Net income	0	0
Other comprehensive income (loss)	11,041	2,555
Deferred Compensation Plan	0
Partners' Capital Account, Contributions		0
Partners' Capital Account, Distributions	0	0
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company	0
Common unit issued as a result of common stock issued by Parent Company, net of purchases	0
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	0	0
Common unit redeemed as result of common stock redeemed by parent		0
Limited Partner [Member]
Dividends, Preferred Stock, Cash		0
Shareholders' Equity	10,847	(2,063)
Net income	111	(19)
Other comprehensive income (loss)	23	2
Deferred Compensation Plan	0
Partners' Capital Account, Contributions		0
Partners' Capital Account, Distributions	194	79
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company	0
Common unit issued as a result of common stock issued by Parent Company, net of purchases	0
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	0	0
Common unit redeemed as result of common stock redeemed by parent		0
General Partner [Member]
Dividends, Preferred Stock, Cash		3,241
Shareholders' Equity	6,559,537	6,747,139
Net income	52,660	(21,367)
Other comprehensive income (loss)	0	0
Deferred Compensation Plan	(3)
Partners' Capital Account, Contributions		0
Partners' Capital Account, Distributions	95,207	(53,400)
Common units repurchased and retired as a result of common stock repurchased and retired by Parent Company	(124,989)
Common unit issued as a result of common stock issued by Parent Company, net of purchases	(6,275)
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	4,121	3,733
Common unit redeemed as result of common stock redeemed by parent		4,461,767
Partnership Interest [Member]
Net income	53,465	(20,715)
Other comprehensive income (loss)	11,524	2,618
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest	459	63
AOCI Attributable to Parent [Member]
Other comprehensive income (loss)	$ 11,041	$ 2,554