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	$ 143,627	$ 132,511	$ 130,006
Other comprehensive income (loss), net of tax:
Net gains arising during the period	5,682	1,513	12,637
Less reclassification adjustment for net gains included in net income	(1,545)	(19,674)	(7,330)
Total	4,137	(18,161)	5,307
Non-credit impairment losses on available for sale and held to maturity securities
Net change in non-credit impairment losses on securities	9,942	(26,656)	3,328
Less reclassification adjustment for credit impairment losses included in net income	2,449	11,633	2,741
Total	12,391	(15,023)	6,069
Unrealized gains and losses on derivatives (cash flow hedges)
Net (losses) gains on derivatives arising during the period	(3,351)	(14,157)	866
Less reclassification adjustment for net losses included in net income	3,760	1,780	1,142
Total	409	(12,377)	2,008
Defined benefit pension plan
Amortization of prior service cost	38	(348)	518
Amortization of net loss	(5,443)	(11,509)	195
Total	(5,405)	(11,161)	713
Total other comprehensive income (loss)	11,532	(56,722)	14,097
Total comprehensive income	$ 155,159	$ 75,789	$ 144,103