Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net Income	$ 36,680	$ 39,596	$ 76,716	$ 81,379
Other Comprehensive Income (Loss), net of tax:
Unrealized gain (loss) on securities	(12,008)	12,990	(2,016)	26,923
Reclassification adjustment for postretirement amendment gains included in net income	0	0	0	(944)
Reclassification adjustment for securities gains included in net income	(1,569)	(723)	(4,264)	(723)
Non-credit related unrealized gain on other-than-temporarily impaired debt securities	0	323	125	512
Unrealized gain on derivative financial instruments	34	34	68	68
Unrecognized postretirement income arising due to plan amendment	0	0	0	2,144
Amortization of net unrecognized pension and postretirement items	466	104	932	200
Other Comprehensive Income (Loss)	(13,077)	12,728	(5,155)	28,180
Total Comprehensive Income	$ 23,603	$ 52,324	$ 71,561	$ 109,559