Stockholders' Equity - Summary of Shares Repurchased Under Stock Purchase Program (Detail) - $ / shares	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Summary Of Shares Repurchased Under Stock Purchase Program [Abstract]
Number of shares repurchased	200,000	56,894
Average price of shares repurchased	$ 27.62	$ 29.10
Shares remaining to be repurchased	300,000	332,552	300,000

Summary of shares repurchased under stock purchase program.

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- Definition

Number of stock bought back by the entity at the exercise price or redemption price.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

+ Details

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- Definition

The remaining number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

+ 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://www.xbrl.org/2003/role/presentationRef
-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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