Total DRIP shares issued under the Plan.

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Executive Incentive Plan, Cash-based Award

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Percentage employer matches of employee contribution.

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value

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Share-based Compensation Arrangement by Share-based Payment Award, Number of Executive Officers Granted Awards

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Value of performance-based awards released.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Subparagraph (SAB TOPIC 14.F)
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-Name Staff Accounting Bulletin (SAB)
-Number Topic 14
-Section F

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The amount of the cost recognized during the period for defined contribution plans.

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-SubTopic 70
-Section 50
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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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No definition available.

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Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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-Paragraph 2
-Subparagraph (j)
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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.

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Discount rate from fair value on offering date that participants pay for shares.

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Discount rate from fair value on purchase date that participants pay for shares.

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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).

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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Number of share instruments newly issued under a share-based compensation plan.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

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No definition available.

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Number of shares issued during the period from a dividend reinvestment plan (DRIP). A dividend reinvestment plan allows the shareholders to reinvest dividends paid to them by the entity on new issues of stock by the entity.

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Number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of any shares forfeited. Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 29, 30
-Article 5

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Stock and Other Incentive Plans (Details Textual)				3 Months Ended			12 Months Ended
Stock and Other Incentive Plans (Details Textual)	Feb. 16, 2016 USD ($) executive_officer shares	Dec. 18, 2015 USD ($) executive_officer shares	Jul. 31, 2012	Mar. 31, 2015 USD ($) shares	Mar. 31, 2014 USD ($) executive_officer shares	Mar. 31, 2013 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) executive_officer shares	Dec. 31, 2013 USD ($) executive_officer shares
401(k) Plan [Abstract]
Percentage of matching contribution												3.00%
Value of matching contribution \| $												$ 400,000	$ 400,000	$ 400,000
Discount on market price on the date of grant												85.00%
Discount on market price on the date of exercise												85.00%
2015 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorization of common shares to issue												3,500,000
Common shares issued, net of forfeitures												139,520
Number of shares authorized												3,360,480
Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares issued, net of forfeitures												1,878,637	1,816,580	1,693,266
Number of shares authorized													573,692	697,006
Granted in period (in shares)												251,789	269,129	134,752
Stock Incentive Plan [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period												3 years
Share-based compensation expense \| $												$ 1,000,000	$ 500,000	$ 600,000
Shares issued under the plan												23,201	26,677	20,256
Stock Incentive Plan [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense \| $												$ 4,900,000	$ 3,600,000	$ 4,300,000
Withheld of common stock												49,225	371,017	18,118
Stock Incentive Plan [Member] \| Restricted Stock [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period												3 years
Stock Incentive Plan [Member] \| Restricted Stock [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period												8 years
Stock Incentive Plan [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of performance based awards released \| $				$ 1,000,000	$ 600,000
Shares issued under the plan				33,145	27,094								0
Stock Incentive Plan [Member] \| Performance Shares [Member] \| Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					8 years
Number of executive officers granted awards \| executive_officer					3
Shares issued under the plan					2,968
Stock Incentive Plan [Member] \| Performance Shares [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					3 years
Stock Incentive Plan [Member] \| Performance Shares [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					8 years
Stock Incentive Plan [Member] \| Performance Shares [Member] \| Weighted Average [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					6 years
Stock Incentive Plan [Member] \| Restricted Stock and Performance Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average amortization period remaining												3 years 7 months 6 days
Stock Incentive Plan [Member] \| Restricted Stock and Performance Based Awards [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period												1 year
Stock Incentive Plan [Member] \| Restricted Stock and Performance Based Awards [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period												8 years
Executive Incentive Plan [Member] \| Performance Shares [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shareholder return performance period used to measure award			1 year
Executive Incentive Plan [Member] \| Performance Shares [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shareholder return performance period used to measure award			3 years
Executive Incentive Plan [Member] \| 2015 Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		3 years
Granted in period \| $		$ 3,900,000
Granted in period (in shares)		139,000
Executive Incentive Plan [Member] \| 2015 Performance Shares [Member] \| Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of executive officers granted awards \| executive_officer		5
Executive Incentive Plan [Member] \| 2015 Performance Shares [Member] \| Senior Vice President [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of executive officers granted awards \| executive_officer		5
Executive Incentive Plan [Member] \| 2014 Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period													3 years
Share-based compensation expense \| $				$ 1,300,000
Granted in period \| $													$ 3,900,000
Granted in period (in shares)													140,930
Executive Incentive Plan [Member] \| 2014 Performance Shares [Member] \| Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of executive officers granted awards \| executive_officer													5
Executive Incentive Plan [Member] \| 2014 Performance Shares [Member] \| Senior Vice President [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of executive officers granted awards \| executive_officer													5
Executive Incentive Plan [Member] \| 2013 Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period														3 years
Share-based compensation expense \| $				$ 900,000	$ 300,000
Granted in period \| $						$ 1,000,000
Granted in period (in shares)														47,709
Executive Incentive Plan [Member] \| 2013 Performance Shares [Member] \| Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of executive officers granted awards \| executive_officer														5
Executive Incentive Plan [Member] \| 2013 Performance Shares [Member] \| Senior Vice President [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of executive officers granted awards \| executive_officer														6
Salary Deferral Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under the plan												55,923	71,460	66,787
Maximum salary deferral for officers under the plan, percent												50.00%
Dividend Reinvestment Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorization of common shares to issue												1,000,000
401(k) Plan [Abstract]
Total DRIP shares issued under the Plan												546,021
Total shares issued under the Dividend Reinvestment Plan												13,950	12,606	16,422
Employees Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized												96,977	88,495	142,367
401(k) Plan [Abstract]
Value of shares available for grant each year \| $												$ 25,000
Discount on market price on the date of grant												85.00%
Discount on market price on the date of exercise												85.00%
Option expiration period												27 months
Cash received from employees upon exercising options \| $												$ 900,000	$ 1,200,000	$ 1,300,000
Deferral Option One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Salary Deferral Plan employer matching contribution, percent												30.00%
Deferral Option One [Member] \| Salary Deferral Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period												3 years
Deferral Option Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Salary Deferral Plan employer matching contribution, percent												50.00%
Deferral Option Two [Member] \| Salary Deferral Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period												5 years
Deferral Option Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Salary Deferral Plan employer matching contribution, percent												100.00%
Deferral Option Three [Member] \| Salary Deferral Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period												8 years
Scenario, Forecast [Member] \| Executive Incentive Plan [Member] \| February 2016 Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense \| $							$ 0	$ 700,000	$ 0	$ 0	$ 1,100,000
Scenario, Forecast [Member] \| Executive Incentive Plan [Member] \| 2015 Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense \| $									$ 1,300,000	1,300,000	1,300,000
Scenario, Forecast [Member] \| Executive Incentive Plan [Member] \| 2014 Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense \| $										$ 1,300,000	1,300,000
Scenario, Forecast [Member] \| Executive Incentive Plan [Member] \| 2013 Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense \| $											$ 900,000
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Executive Incentive Plan, Cash-based Award \| $	$ 1,100,000
Subsequent Event [Member] \| Executive Incentive Plan [Member] \| February 2016 Cash Incentive and Performance-based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted in period \| $	$ 5,800,000
Subsequent Event [Member] \| Executive Incentive Plan [Member] \| February 2016 Cash Incentive and Performance-based Awards [Member] \| Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of executive officers granted awards \| executive_officer	5
Subsequent Event [Member] \| Executive Incentive Plan [Member] \| February 2016 Cash Incentive and Performance-based Awards [Member] \| Senior Vice President [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of executive officers granted awards \| executive_officer	5
Subsequent Event [Member] \| Executive Incentive Plan [Member] \| February 2016 Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted in period \| $	$ 4,700,000
Granted in period (in shares)	163,788
Subsequent Event [Member] \| 3-year Vesting [Member] \| Executive Incentive Plan [Member] \| February 2016 Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Subsequent Event [Member] \| 5-year Vesting [Member] \| Executive Incentive Plan [Member] \| February 2016 Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years