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Employee Benefit Plans (Details) | 12 Months Ended
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Dec. 31, 2016 USD ($) installment $ / shares shares | Dec. 31, 2015 USD ($) $ / shares shares | Dec. 31, 2014 USD ($) $ / shares shares
Defined Benefit Plan Disclosure |  |  |
Employer contribution for defined contribution plan | $ 2,000,000 | $ 1,000,000 | $ 900,000
Employee Stock Ownership Plan, common stock, shares outstanding (shares) | shares | 149,050.91 |  |
Employee Stock Ownership Plan, common stock, fair value | $ 14,600,000 |  |
Outside Directors |  |  |
Defined Benefit Plan Disclosure |  |  |
Number of deferred common stock (shares) | shares | 10,166 | 8,466 | 9,415
Weighted-average grant date fair values of deferred common stock (dollars per share) | $ / shares | $ 97.99 | $ 78.62 | $ 70.63
Nonqualified Deferred Compensation Plan |  |  |
Defined Benefit Plan Disclosure |  |  |
Deferred compensation expense | $ 96,000 | $ 106,000 | $ 82,000
Number of annual installments of deferred compensation (installment) | installment | 2 |  |
Number of days after departure from board of directors for payment of deferred compensation (days) | 90 days |  |

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- Definition The compensation expense recognized during the period pertaining to the deferred compensation arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 710 -SubTopic 10 -Section 30 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363 + Details
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- Definition The amount of the cost recognized during the period for defined contribution plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Definition Fair value of unearned shares held by the employee stock ownership plan (ESOP). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Fair Value -URI http://asc.fasb.org/extlink&oid=51653337 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 40 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=65895303&loc=d3e17540-113929 + Details
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- Definition Sum of the allocated, committed-to-be-released and suspense shares of the entity held by the plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 40 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=65895303&loc=d3e17540-113929 + Details
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