Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income	$ 81,127	$ 87,888	$ 94,577
Other comprehensive income (loss):
Increase (decrease) in net unrealized gains on securities available for sale	5,557	19,282	(6,197)
Deferred tax expense	(2,337)	(8,108)	2,606
Increase (decrease) in net unrealized gains on securities available for sale, net of tax	3,220	11,174	(3,591)
Post-retirement benefit transition obligation amortization	61	61	61
Deferred tax expense	(25)	(25)	(25)
Post-retirement benefit transition obligation amortization, net of tax	36	36	36
Total other comprehensive income (loss)	3,256	11,210	(3,555)
Total comprehensive income	$ 84,383	$ 99,098	$ 91,022