Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Consolidated Statements of Comprehensive Income (Unaudited) [Abstract]
Net income per consolidated statements of income	$ 28,430	$ 33,589	$ 88,180	$ 95,489
Unrealized gains (losses) on available for sale securities and transferred securities:
Unrealized holding gains (losses) arising during the period	11,035	(5,182)	8,470	5,814
Less: adjustment for net losses (gains) realized in net income	0	55	0	(185)
Change in net unrealized holding loss on securities transferred to held to maturity	1,036	1,011	2,931	2,744
Pension and other postretirement benefit plans:
Net change in prior service costs	39	39	116	116
Recognized net loss due to lump sum settlement	373	1,055	926	1,518
Change in net actuarial loss	751	(949)	2,256	166
Derivatives:
Change in the accumulated loss on effective cash flow hedge derivatives	(751)	163	(1,185)	(807)
Less: adjustment for loss realized in net income	130	0	390	0
Other comprehensive income (loss), net of tax	12,613	(3,808)	13,904	9,366
Comprehensive income	$ 41,043	$ 29,781	$ 102,084	$ 104,855