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Investment Securities
12 Months Ended
Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]  
Investment Securities
INVESTMENT SECURITIES

The amortized cost and approximate fair values of investment securities are summarized as follows:
December 31, 2012
Amortized
Cost
Gross
Unrealized
Gains
Gross
Unrealized
Losses
Estimated
Fair
Value
Available-for-Sale
 
 
 
 
Obligations of U.S. government agencies
$
751,501

$
3,518

$
(163
)
$
754,856

U.S. agency residential mortgage-backed securities &
   collateralized mortgage obligations
1,214,377

27,000

(1,526
)
1,239,851

Private mortgage-backed securities
539

13

(1
)
551

Total
$
1,966,417

$
30,531

$
(1,690
)
$
1,995,258

December 31, 2012
Amortized
Cost
Gross
Unrealized
Gains
Gross
Unrealized
Losses
Estimated
Fair
Value
Held-to Maturity
 
 
 
 
State, county and municipal securities
$
192,875

$
10,835

$
(176
)
$
203,534

Corporate securities
14,975

64

(13
)
15,026

Other securities
373



373

Total
$
208,223

$
10,899

$
(189
)
$
218,933



Gross gains of $351 and gross losses of $3 were realized on the disposition of available-for-sale securities in 2012.
December 31, 2011
Amortized
Cost
Gross
Unrealized
Gains
Gross
Unrealized
Losses
Estimated
Fair
Value
Available-for-Sale
 
 
 
 
Obligations of U.S. government agencies
$
1,134,427

$
4,353

$
(662
)
$
1,138,118

U.S. agency residential mortgage-backed securities &
   collateralized mortgage obligations
848,444

29,567

(14
)
877,997

Private mortgage-backed securities
758

7

(16
)
749

Total
$
1,983,629

$
33,927

$
(692
)
$
2,016,864

December 31, 2011
Amortized
Cost
Gross
Unrealized
Gains
Gross
Unrealized
Losses
Estimated
Fair
Value
Held-to Maturity
 
 
 
 
State, county and municipal securities
$
152,619

$
9,113

$
(17
)
$
161,715

Other securities
162



162

Total
$
152,781

$
9,113

$
(17
)
$
161,877



Gross gains of $1,544 were realized on the disposition of available-for-sale securities in 2011. No gross losses were realized on the disposition of available-for-sale securities in 2011. Gross gains of $173 and gross losses of $3 were realized on the disposition of available-for-sale securities in 2010.

As of December 31, 2012, the Company had general obligation securities with amortized costs of $139,434 included in state, county and municipal securities, of which $67,171 were issued by political subdivisions or agencies within the states of Montana, Wyoming and South Dakota.

The following table shows the gross unrealized losses and fair values of investment securities, aggregated by investment category, and the length of time individual investment securities have been in a continuous unrealized loss position, as of December 31, 2012 and 2011.
 
Less than 12 Months
12 Months or More
Total
December 31, 2012
Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Available-for-Sale
 
 
 
 
 
 
Obligations of U.S. government agencies
$
93,982

$
(163
)
$

$

$
93,982

$
(163
)
U.S. agency residential mortgage-backed
   securities & collateralized mortgage
   obligations
250,198

(1,526
)


250,198

(1,526
)
Private mortgage-backed securities


137

(1
)
137

(1
)
Total
$
344,180

$
(1,689
)
$
137

$
(1
)
$
344,317

$
(1,690
)
 
Less than 12 Months
12 Months or More
Total
December 31, 2012
Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Held-to-Maturity
 
 
 
 
 
 
State, county and municipal securities
$
19,389

$
(168
)
$
557

$
(8
)
$
19,946

$
(176
)
Corporate securities
9,312

(13
)


9,312

(13
)
Total
$
28,701

(181
)
557

(8
)
29,258

(189
)
 
Less than 12 Months
12 Months or More
Total
December 31, 2011
Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Available-for-Sale
 
 
 
 
 
 
Obligations of U.S. government agencies
$
287,404

$
(662
)
$

$

$
287,404

$
(662
)
U.S. agency residential mortgage-backed
   securities & collateralized mortgage
   obligations
45,694

(14
)


45,694

(14
)
Private mortgage-backed securities
246

(10
)
177

(6
)
423

(16
)
Total
$
333,344

$
(686
)
$
177

$
(6
)
$
333,521

$
(692
)
 
Less than 12 Months
12 Months or More
Total
December 31, 2011
Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Fair
Value
Gross
Unrealized
Losses
Held-to-Maturity
 
 
 
 
 
 
State, county and municipal securities
$

$

$
773

$
(17
)
$
773

$
(17
)


The investment portfolio is evaluated quarterly for other-than-temporary declines in the market value of each individual investment security. Consideration is given to the length of time and the extent to which the fair value has been less than cost; the financial condition and near term prospects of the issuer; and, the intent and ability of the Company to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value. As of December 31, 2012, the Company had 69 individual investment securities that were in an unrealized loss position. As of December 31, 2011, the Company had 24 individual investment securities that were in an unrealized loss position. Unrealized losses as of December 31, 2012 and 2011 related primarily to fluctuations in the current interest rates. The fair value of these investment securities is expected to recover as the securities approach their maturity or repricing date or if market yields for such investments decline. As of December 31, 2012, the Company had the intent and ability to hold these investment securities for a period of time sufficient to allow for an anticipated recovery. Furthermore, the Company does not have the intent to sell any of the available-for-sale securities in the above table and it is more likely than not that the Company will not have to sell any such securities before a recovery in cost. No impairment losses were recorded during 2012, 2011 or 2010.

Maturities of investment securities at December 31, 2012 are shown below. Maturities of mortgage-backed securities have been adjusted to reflect shorter maturities based upon estimated prepayments of principal. All other investment securities maturities are shown at contractual maturity dates.
 
Available-for-Sale
 
Held-to-Maturity
December 31, 2012
Amortized
Cost
Estimated
Fair Value
 
Amortized
Cost
Estimated
Fair Value
Within one year
$
438,770

$
445,319

 
$
4,657

$
4,657

After one year but within five years
1,042,696

1,056,854

 
47,437

48,293

After five years but within ten years
351,310

356,641

 
86,416

90,954

After ten years
133,641

136,444

 
69,340

74,656

Total
1,966,417

1,995,258

 
207,850

218,560

Investments with no stated maturity


 
373

373

Total
$
1,966,417

$
1,995,258

 
$
208,223

$
218,933



At December 31, 2012, the Company had investment securities callable within one year with amortized costs and estimated fair values of $370,546 and $371,280, respectively. These investment securities are primarily classified as available-for-sale and included in the after one year but within five years category in the table above.

At December 31, 2012, the Company had callable structured notes with amortized costs and estimated fair values of $148,428 and $148,778, respectively. These callable structured notes, which are classified as available-for-sale and included in the after one year but within five years category in the table above, have fixed interest rates that increase at various intervals as market rates increase.

Maturities of securities do not reflect rate repricing opportunities present in adjustable rate mortgage-backed securities. At December 31, 2012 and 2011, the Company had variable rate mortgage-backed securities with amortized costs of $29,105 and $21,333, respectively, classified as available-for-sale in the table above.

There are no significant concentrations of investments at December 31, 2012, (greater than 10 percent of stockholders’ equity) in any individual security issuer, except for U.S. government or agency-backed securities. As of December 31, 2012 and 2011, all mortgage-backed securities were residential in nature.

Investment securities with amortized cost of $1,318,807 and $1,280,317 at December 31, 2012 and 2011, respectively, were pledged to secure public deposits and securities sold under repurchase agreements. The approximate fair value of securities pledged at December 31, 2012 and 2011 was $1,344,220 and $1,310,895, respectively. All securities sold under repurchase agreements are with customers and mature on the next banking day. The Company retains possession of the underlying securities sold under repurchase agreements.