Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net Income	$ 40,036us-gaap_NetIncomeLoss	$ 41,783us-gaap_NetIncomeLoss
Other Comprehensive Income, net of tax:
Unrealized gain on securities	9,992	13,933
Reclassification adjustment for postretirement amendment gains included in net income	0	(944)
Reclassification adjustment for securities gains included in net income	(2,695)	0
Non-credit related unrealized gain on other-than-temporarily impaired debt securities	125	189
Unrealized gain on derivative financial instruments	34	34
Unrecognized postretirement income arising due to plan amendment	0	2,144
Amortization of net unrecognized pension and postretirement items	466	96
Other Comprehensive Income	7,922	15,452
Total Comprehensive Income	$ 47,958us-gaap_ComprehensiveIncomeNetOfTax	$ 57,235us-gaap_ComprehensiveIncomeNetOfTax

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount after tax of (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit.

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Amount after tax of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans.

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Amount after tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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Amount after tax of other than temporary impairment loss (OTTI) on investments in available-for-sale and held-to-maturity debt securities, recognized in other comprehensive loss and attributable to parent entity.

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