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Employee Benefit Plans (Tables) | 6 Months Ended
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Jun. 30, 2017
BancShares Plan |
Defined Benefit Plan Disclosure [Line Items] |
Schedule of Net Benefit Costs | BancShares Plan For the three and six months ended June 30, 2017 and 2016, the components of net periodic benefit cost are as follows:
| Three months ended June 30 |  | Six months ended June 30
(Dollars in thousands) | 2017 |  | 2016 |  | 2017 |  | 2016
Service cost | $ | 2,934 |  |  | $ | 3,090 |  |  | $ | 6,310 |  |  | $ | 6,310 |
Interest cost | 7,069 |  |  | 7,269 |  |  | 14,449 |  |  | 14,450 |
Expected return on assets | (10,307 | ) |  | (9,167 | ) |  | (21,005 | ) |  | (18,326 | )
Amortization of prior service cost | 53 |  |  | 52 |  |  | 105 |  |  | 104 |
Amortization of net actuarial loss | 2,193 |  |  | 1,830 |  |  | 4,427 |  |  | 3,430 |
Net periodic benefit cost | $ | 1,942 |  |  | $ | 3,074 |  |  | $ | 4,286 |  |  | $ | 5,968 |
Bancorporation Plan |
Defined Benefit Plan Disclosure [Line Items] |
Schedule of Net Benefit Costs | Bancorporation Plan For the three and six months ended June 30, 2017 and 2016, the components of net periodic benefit cost are as follows:
| Three months ended June 30 |  | Six months ended June 30
(Dollars in thousands) | 2017 |  | 2016 |  | 2017 |  | 2016
Service cost | $ | 670 |  |  | $ | 633 |  |  | $ | 1,341 |  |  | $ | 1,283 |
Interest cost | 1,682 |  |  | 1,713 |  |  | 3,365 |  |  | 3,388 |
Expected return on assets | (2,796 | ) |  | (2,771 | ) |  | (5,592 | ) |  | (5,550 | )
Amortization of net actuarial loss | 214 |  |  | — |  |  | 428 |  |  | — |
Net periodic benefit cost | $ | (230 | ) |  | $ | (425 | ) |  | $ | (458 | ) |  | $ | (879 | )

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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