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Stock-Based Compensation - Schedule of Information Related to Outstanding SOSARS (Detail) - Stock Only Stock Appreciation Rights (SOSARs) [Member] - USD ($) $ / shares in Units, $ in Thousands | 9 Months Ended
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Sep. 30, 2017 | Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Beginning Balance, Outstanding | 2,736,616 | 2,199,742
Granted |  | 743,925
Exercised | (33,050) | (61,190)
Canceled / forfeited | (17,630) | (143,932)
Ending Balance, Outstanding | 2,685,936 | 2,738,545
Beginning Balance, Weighted Average Exercise Price, Outstanding | $ 17.64 | $ 17.82
Weighted Average Exercise Price, Granted |  | 17.54
Weighted Average Exercise Price, Exercised | 14.65 | 10.70
Weighted Average Exercise Price, Canceled / forfeited | 18.46 | 17.87
Ending Balance, Weighted Average Exercise Price, Outstanding | $ 17.67 | 17.64
Weighted average grant date fair value per share |  | $ 4.07
Aggregate grant date fair value |  | $ 3,013
Black-Scholes assumptions |  |
Dividend yield |  | 2.85%
Risk free rate of return |  | 1.34%
Volatility |  | 31.97%
Expected life |  | 6 years

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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + 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 (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + 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 (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Weighted average expected volatility rate of share-based compensation awards. + 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 (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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