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Business Segments Long-Lived Assets (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues | $ 679,035 | $ 667,048 | $ 653,313 | $ 626,528 | $ 620,884 | $ 629,401 | $ 608,088 | $ 582,040 | $ 2,625,924 | $ 2,440,413 | $ 2,065,008
Long-Lived Assets | 57,996 |  |  |  | 56,942 |  |  |  | 57,996 | 56,942 |
Domestic [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 2,494,446 | 2,324,713 | 1,972,888
Long-Lived Assets | 56,137 |  |  |  | 55,801 |  |  |  | 56,137 | 55,801 |
Foreign [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 131,478 | 115,700 | $ 92,120
Long-Lived Assets | $ 1,859 |  |  |  | $ 1,141 |  |  |  | $ 1,859 | $ 1,141 |

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- Definition Long-lived assets other than financial instruments, long-term customer relationships of a financial institution, mortgage and other servicing rights, deferred policy acquisition costs, and deferred tax assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 41 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e9038-108599 + Details
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- Definition Aggregate revenue during the period from services rendered in the normal course of business, after deducting allowances and discounts. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1(d)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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