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v3.8.0.1

Changes in Option Awards All of Which Related to Common Stock (Detail) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Weighted-Avg. Per Share Exercise Price, beginning period | $ 21.69 |  |
Weighted-Avg. Per Share Exercise Price, ending period | 27.73 | $ 21.69 |
Weighted-Avg. Per Share Exercisable Price, ending period | $ 20.48 |  |
Outstanding, Beginning Balance | 2,664,333 | 2,653,558 | 3,154,006
Outstanding, Ending Balance | 2,263,126 | 2,664,333 | 2,653,558
Exercisable at End of Period | 1,387,259 | 1,602,651 | 1,544,186
Minimum |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Weighted-Avg. Per Share Exercise Price - Granted | $ 50.16 | $ 31.49 | $ 23.24
Weighted-Avg. Per Share Exercise Price - Exercised | 4.75 | 4.75 | 4.10
Weighted-Avg. Per Share Exercise Price - Forfeited | 30.77 | 23.24 | 17.46
Weighted-Avg. Per Share Exercise Price, ending period | 4.75 |  |
Maximum |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Weighted-Avg. Per Share Exercise Price - Granted | 50.16 | 46.93 | 25.34
Weighted-Avg. Per Share Exercise Price - Exercised | 31.67 | 30.77 | 17.46
Weighted-Avg. Per Share Exercise Price - Forfeited | 50.16 | $ 46.93 | $ 23.24
Weighted-Avg. Per Share Exercise Price, ending period | $ 50.16 |  |
Two Thousand Seventeen |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Granted | 358,150 |  |
Exercised | (752,603) |  |
Forfeited | (6,754) |  |
Aggregate Intrinsic Value, Exercised at end of Period | $ 12.7 |  |
Two Thousand Sixteen |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Granted |  | 553,370 |
Exercised |  | (531,933) |
Forfeited |  | (10,662) |
Aggregate Intrinsic Value, Exercised at end of Period |  | $ 7.5 |
Two Thousand Fifteen |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Granted |  |  | 484,990
Exercised |  |  | (978,208)
Forfeited |  |  | (7,230)
Aggregate Intrinsic Value, Exercised at end of Period |  |  | $ 10.2

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- Definition The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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