Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Partners' Capital [Abstract]
Net income	$ 60,444	$ 58,669	$ 175,295	$ 177,764
Other comprehensive income (loss), before tax:
Change in net unrealized gain/loss during the period	(551)	40,122	(95,920)	62,972
Change in net unrealized gain on securities transferred to held to maturity	(8,054)	0	(26,258)	0
Reclassification adjustment for net (gains) losses included in net income	14	0	3	121
Total securities available for sale and transferred securities	(8,591)	40,122	(122,175)	63,093
Defined-benefit post-retirement benefit plans:
Change in the net actuarial gain/loss	1,640	1,427	4,919	4,084
Derivatives:
Change in the accumulated gain/loss on effective cash flow hedge derivatives	(15)	(269)	(48)	(760)
Reclassification adjustments for (gains) losses included in net income:
Interest rate swaps on variable-rate loans	(9,345)	(9,345)	(28,035)	(28,035)
Interest rate swap on junior subordinated deferrable interest debentures	1,120	1,063	3,308	3,140
Total derivatives	(8,240)	(8,551)	(24,775)	(25,655)
Other comprehensive income (loss), before tax	(15,191)	32,998	(142,031)	41,522
Deferred tax expense (benefit) related to other comprehensive income	(5,316)	11,550	(49,710)	14,533
Other comprehensive income (loss), net of tax	(9,875)	21,448	(92,321)	26,989
Comprehensive income	$ 50,569	$ 80,117	$ 82,974	$ 204,753