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Subsequent Events - Additional Information (Detail) - USD ($) | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Feb. 28, 2019 | Jan. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Oct. 27, 2016
Subsequent Event [Line Items] |  |  |  |  |  |
Payments for repurchase of additional shares |  |  | $ 161,034,000 |  |  |
Class A Common Stock [Member] |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Average price per share |  |  | $ 40.43 | $ 0 | $ 0 |
Authorized share repurchase term |  |  | 3 years |  |  |
Class A Common Stock [Member] | Maximum [Member] |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Authorized share repurchase amount |  |  |  |  |  | $ 250,000,000
Subsequent Event [Member] | Class A Common Stock [Member] |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Payments for repurchase of additional shares |  | $ 45,100,000 |  |  |  |
Shares repurchased during the period |  | 1,144,449 |  |  |  |
Average price per share |  | $ 39.38 |  |  |  |
Authorized share repurchase term | 3 years |  |  |  |  |
Subsequent Event [Member] | Class A Common Stock [Member] | Maximum [Member] |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |
Authorized share repurchase amount | $ 300,000,000 |  |  |  |  |

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- Definition The cash outflow to reacquire common stock during the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585 + Details
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- Definition Amount of stock repurchase plan authorized. + References No definition available. + Details
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- Definition Period which shares may be purchased under a stock repurchase plan authorized by an entity's Board of Directors, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -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 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -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 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -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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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
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- Definition Total cost of shares repurchased divided by the total number of shares repurchased. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
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- Details
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- Details
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