Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement of Partners' Capital [Abstract]
Net income	$ 66,470	$ 59,663	$ 127,658	$ 114,851
Other comprehensive income (loss), before tax:
Change in net unrealized gain/loss during the period	45,112	(74,025)	66,543	(95,369)
Change in net unrealized gain on securities transferred to held to maturity	(9,175)	(9,745)	(18,373)	(18,204)
Reclassification adjustment for net (gains) losses included in net income	(2)	(6)	(2)	(11)
Total securities available for sale and transferred securities	35,935	(83,776)	48,168	(113,584)
Defined-benefit post-retirement benefit plans:
Change in the net actuarial gain/loss	671	1,639	1,343	3,279
Derivatives:
Change in the accumulated gain/loss on effective cash flow hedge derivatives	0	(33)	0	(33)
Reclassification adjustments for (gains) losses included in net income:
Interest rate swaps on variable-rate loans	(9,345)	(9,345)	(18,690)	(18,690)
Interest rate swap on junior subordinated deferrable interest debentures	0	1,103	0	2,188
Total derivatives	(9,345)	(8,275)	(18,690)	(16,535)
Other comprehensive income (loss), before tax	27,261	(90,412)	30,821	(126,840)
Deferred tax expense (benefit) related to other comprehensive income	9,541	(31,644)	10,787	(44,394)
Other comprehensive income (loss), net of tax	17,720	(58,768)	20,034	(82,446)
Comprehensive income	$ 84,190	$ 895	$ 147,692	$ 32,405