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Stock-Based Compensation Plans and Arrangements - Restricted Stock and Performance Stock Unit Activity (Detail) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Weighted Average Grant Date Fair Value |  |  |
Unrecognized compensation cost | $ 12.0 |  |
Weighted average period for total unrecognized compensation cost | 1 year 3 months 15 days |  |
Restricted Stock |  |  |
Number of Shares |  |  |
Beginning balance (in shares) | 81,103 |  |
Granted (in shares) | 84,392 |  |
Vested and converted to common stock (in shares) | (81,103) |  |
Canceled (in shares) | 0 |  |
Ending balance (in shares) | 84,392 | 81,103 |
Weighted Average Grant Date Fair Value |  |  |
Beginning balance (in dollars per share) | $ 10.85 |  |
Granted (in dollars per share) | 11.73 |  |
Vested (in dollars per share) | 10.85 |  |
Canceled (in dollars per share) | 0.00 |  |
Ending balance (in dollars per share) | $ 11.73 | $ 10.85 |
Fair value of shares vested | $ 0.9 | $ 0.8 | $ 0.8
Unrecognized compensation cost | $ 0.5 |  |
Weighted average period for total unrecognized compensation cost | 5 months 22 days |  |
Restricted Stock Units And Performance Stock Units |  |  |
Number of Shares |  |  |
Beginning balance (in shares) | 5,945,290 |  |
Granted (in shares) | 2,522,075 |  |
Vested and converted to common stock (in shares) | (3,023,152) |  |
Canceled (in shares) | (106,179) |  |
Ending balance (in shares) | 5,338,034 | 5,945,290 |
Weighted Average Grant Date Fair Value |  |  |
Beginning balance (in dollars per share) | $ 8.60 |  |
Granted (in dollars per share) | 11.61 |  |
Vested (in dollars per share) | 8.37 |  |
Canceled (in dollars per share) | 10.62 |  |
Ending balance (in dollars per share) | $ 10.11 | $ 8.60 |
Fair Value Of Restricted Stock Units That Vested And Converted To Common Stock | $ 25.3 | $ 29.2 | $ 22.2
Unrecognized compensation cost | $ 11.2 |  |
Weighted average period for total unrecognized compensation cost | 1 year 4 months 15 days |  |

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- Definition Share based compensation arrangement by share based payment award equity instruments other than options canceled forfeited in period weighted average grant date fair value. + References No definition available. + Details
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- Definition Unrecognized cost of unvested share-based compensation awards. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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=109197908&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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