Comprehensive Income (Components of Comprehensive Income-Gross and Net of Tax) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net income, Gross	$ 65,839	$ 75,326	$ 168,894	$ 139,931
Unrealized holding gains (losses) during the period, Gross	8,371	(13,831)	(27,896)	64,255
Amounts reclassified into net income: HTM securities, Gross	(97)	(373)	(543)	(1,050)
Amounts reclassified into net income: Non-credit OTTI, Gross		1,200	357	1,669
Realized gains on AFS securities, Gross	(305)	(16,435)	(16,778)	(28,672)
Net unrealized gains (losses), Gross	7,969	(29,439)	(44,860)	36,202
Amount reclassified into net income: Net actuarial loss, Gross	1,709	381	5,127	1,142
Defined pension and other post-retirement benefit plans, Gross	1,709	381	5,127	1,142
Other comprehensive income (loss), Gross	9,678	(29,058)	(39,733)	37,344
Comprehensive income before tax	75,517	46,268	129,161	177,275
Net income, Tax	18,843	22,164	48,422	39,454
Unrealized holding gains (losses) during the period, Tax	2,929	(4,843)	(9,764)	22,488
Amounts reclassified into net income: HTM securities, Tax	(34)	(130)	(190)	(367)
Amounts reclassified into net income: Non-credit OTTI, Tax		420	125	584
Realized gains on AFS securities, Tax	(106)	(5,752)	(5,872)	(10,035)
Net unrealized gains (losses), Tax	2,789	(10,305)	(15,701)	12,670
Amount reclassified into net income: Net actuarial loss, Tax	599	134	1,795	400
Defined pension and other post-retirement benefit plans, Tax	599	134	1,795	400
Other comprehensive income (loss), Tax	3,388	(10,171)	(13,906)	13,070
Comprehensive income Tax	22,231	11,993	34,516	52,524
Net income	46,996	53,162	120,472	100,477
Unrealized holding gains (losses) arising during period	5,442	(8,988)	(18,132)	41,767
Amounts reclassified into net income: HTM Securities	(63)	(243)	(353)	(683)
Amounts reclassified into net income: Non-credit other-than-temporary impairments on disposed securities	0	780	232	1,085
Realized gains on available-for-sale securities	(199)	(10,683)	(10,906)	(18,637)
Total unrealized gains (losses) on investment securities	5,180	(19,134)	(29,159)	23,532
Amount reclassified into net income: Net actuarial loss	1,110	247	3,332	742
Total defined benefit pension and post-retirement plans	1,110	247	3,332	742
Other comprehensive income (loss)	6,290	(18,887)	(25,827)	24,274
Comprehensive income	$ 53,286	$ 34,275	$ 94,645	$ 124,751