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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, 2016 | Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Beginning Balance, Outstanding | 2,199,742 | 1,864,707
Granted | 743,925 | 423,590
Exercised | (61,190) | (70,347)
Canceled / forfeited | (143,932) | (17,559)
Ending Balance, Outstanding | 2,738,545 | 2,200,391
Beginning Balance, Weighted Average Exercise Price, Outstanding | $ 17.82 | $ 16.20
Weighted Average Exercise Price, Granted | 17.54 | 24.62
Weighted Average Exercise Price, Exercised | 10.70 | 14.12
Weighted Average Exercise Price, Canceled / forfeited | 17.87 | 25.24
Ending Balance, Weighted Average Exercise Price, Outstanding | 17.64 | 17.82
Weighted average grant date fair value per share | $ 4.07 | $ 7.46
Aggregate grant date fair value | $ 3,013 | $ 3,134
Black-Scholes assumptions |  |
Dividend yield | 2.85% | 1.94%
Risk free rate of return | 1.34% | 1.64%
Volatility | 31.97% | 36.38%
Expected life | 6 years | 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=6415400&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=6415400&loc=d3e5070-113901 + Details
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