Consolidated Statements of Comprehensive Income (Loss) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income, Before-tax Amount	$ 73,950	$ 72,906	$ 150,975	$ 119,459
Net income, Tax (Expense) Benefit	(27,078)	(27,371)	(55,686)	(44,350)
Net income, Net of Tax Amount	46,872	45,535	95,289	75,109
Reclassification adjustment for losses realized in net income, Before-tax Amount	112	112	224	224
Reclassification adjustment for losses realized in net income, Tax (Expense) Benefit	(44)	(45)	(87)	(88)
Reclassification adjustment for losses realized in net income, Net of Tax Amount	68	67	137	136
Net unrealized gains/losses on investment securities available for sale: Before-tax Amount
Reclassification adjustment for net gains realized in net income, Before-tax Amount	0	(1,403)	(1,331)	(1,448)
Net unrealized gains (losses) arising during the period, Before-tax Amount	26,797	(57,850)	45,640	(60,014)
Net unrealized gains (losses), Before-tax Amount	26,797	(59,253)	44,309	(61,462)
Net unrealized gains/losses on investment securities available for sale: Tax (Expense) Benefit
Reclassification adjustment for net gains realized in net income, Tax (Expense) Benefit	0	541	513	557
Net unrealized gains (losses) arising during the period, Tax (Expense) Benefit	(10,317)	22,272	(17,572)	23,105
Net unrealized gains (losses), Tax (Expense) Benefit	(10,317)	22,813	(17,059)	23,662
Net unrealized gains/losses on investment securities available for sale: Net of Tax Amount
Reclassification adjustment for net gains realized in net income, Net of Tax Amount	0	(862)	(818)	(891)
Net unrealized gains (losses) arising during the period, Net of Tax Amount	16,480	(35,578)	28,068	(36,909)
Net unrealized gains (losses), Net of Tax Amount	16,480	(36,440)	27,250	(37,800)
Post-retirement unfunded health benefit: Before-tax Amount
Reclassification adjustment for (gains) losses realized in net income, Before-tax Amount	(72)	0	(144)	(26)
Actuarial gains arising during the period, Before-tax Amount	395	844	395	830
Net unrealized gains, Before-tax Amount	323	844	251	804
Post-retirement unfunded health benefit: Tax (Expense) Benefit
Reclassification adjustment for (gains) losses realized in net income, Tax (Expense) Benefit	28	7	56	10
Actuarial gains arising during the period, Tax (Expense) Benefit	(152)	(325)	(152)	(311)
Net unrealized gains, Tax (Expense) Benefit	(124)	(318)	(96)	(301)
Post-retirement unfunded health benefit: Net of Tax Amount
Reclassification adjustment for (gains) losses realized in net income, Net of Tax Amount	(44)	7	(88)	(16)
Actuarial gains arising during the period, Net of Tax Amount	243	519	243	519
Net unrealized gains, Net of Tax Amount	199	526	155	503
Other comprehensive (loss) income, Before-tax Amount	27,232	(58,297)	44,784	(60,434)
Other comprehensive (loss) income, Tax (Expense) Benefit	(10,485)	22,450	(17,242)	23,273
Other comprehensive (loss) income, Net of Tax Amount	16,747	(35,847)	27,542	(37,161)
Comprehensive income, Net of Tax Amount	$ 63,619	$ 9,688	$ 122,831	$ 37,948