Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Consolidated Statements of Comprehensive Income (Unaudited) [Abstract]
Net income per consolidated statements of income	$ 24,866	$ 30,320
Unrealized gains (losses) on available for sale securities:
Unrealized holding gains (losses) arising during the period	1,380	(1,916)
Less: adjustment for net gains realized in net income	(126)	(648)
Pension and other postretirement benefit plans:
Change in the net actuarial loss during the period	1,060	980
Other comprehensive income (loss), net of tax:	2,314	(1,584)
Comprehensive income	$ 27,180	$ 28,736