Stock-Based Compensation - Vesting and Deferred Compensation Plan (Details) - shares	9 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Restricted stock awards
Stock-based compensation
Vesting period of shares awarded under the Program	3 years
Performance shares
Stock-based compensation
Vesting period of shares awarded under the Program	3 years
Deferred Compensation Equity
Performance share awards
Number of common shares deferred (in shares)	278,096	294,574

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration