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Stockholders' Equity (Tables) | 12 Months Ended
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Dec. 31, 2017
Stockholders' Equity and Common Stock Issued and Outstanding [Abstract] |
Summary of Shares Repurchased |
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﻿ |  | 2015
﻿Purchase of Treasury Stock | $ | 250,000,000
﻿Shares repurchased |  | 5,967,313
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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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