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Capital Stock - Additional Information (Detail) - $ / shares | 3 Months Ended | 12 Months Ended
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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, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Class Of Stock Disclosures [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized capital stock | 485,000,000 |  |  |  | 485,000,000 |  |  |  |  |  |  |  | 485,000,000 | 485,000,000 |
Common stock, shares authorized | 475,000,000 |  |  |  | 475,000,000 |  |  |  |  |  |  |  | 475,000,000 | 475,000,000 |
Preferred stock, shares authorized | 10,000,000 |  |  |  | 10,000,000 |  |  |  |  |  |  |  | 10,000,000 | 10,000,000 |
Common dividends declared per share | $ 0.02 | $ 0.02 | $ 0.02 | $ 0.02 | $ 0.02 | $ 0.02 | $ 0.02 | $ 0.02 | $ 0.04 | $ 0.04 | $ 0.04 | $ 0.04 | $ 0.08 | $ 0.08 | $ 0.16

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- Definition Number of authorized capital units or capital shares. This element is relevant to issuers of face-amount certificates and registered investment companies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-04.16(a)) -URI http://asc.fasb.org/extlink&oid=6488278&loc=d3e603758-122996 + Details
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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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- Definition The maximum number of common shares permitted to be issued by an entity's charter and bylaws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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