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Share Repurchase Program (Tables) | 12 Months Ended
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Dec. 31, 2017
Proceeds from (Repurchase of) Equity [Abstract] |
Schedule of shares repurchased |
| For the Year Ended December 31,
| 2017 |  | 2016
Shares repurchased | 9,301 |  |  | 5,698 |
Average price per share | $ | 233.57 |  |  | $ | 264.21 |
Total investment | $ | 2,172,437 |  |  | $ | 1,505,371 |

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- Definition Tabular disclosure of treasury stock, including, but not limited to, average cost per share, description of share repurchase program, shares repurchased, shares held for each class of treasury stock. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6405834&loc=d3e23315-112656 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6405834&loc=d3e23285-112656 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6405834&loc=d3e23309-112656 + Details
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