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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-Name Accounting Standards Codification
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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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- Definition

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

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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- Definition

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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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Net number of non-option equity instruments granted to participants.

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Stock Based Compensation Plans - Restricted Stock and Employee Share Purchase Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Stock Activity
Discount from market price as of purchase date	15.00%
Restricted Stock Plan [Member]
Restricted Stock Activity
Non-vested shares at beginning of year (in shares)	447,380	471,597	499,463
Granted (in shares)	107,237	123,181	126,946
Vested (in shares)	(131,988)	(113,507)	(108,424)
Canceled (in shares)	(24,419)	(33,891)	(46,388)
Non-vested shares at end of year (in shares)	398,210	447,380	471,597
Share based compensation expense	$ 8,148
Employee Share Purchase Plan [Member]
Restricted Stock Activity
Allocated share-based compensation expense	$ 197	$ 287	$ 147
Shares issued (in shares)	16,989	25,551	23,912
Year one [Member] \| Restricted Stock Plan [Member]
Restricted Stock Activity
Share based compensation expense	$ 3,211
Year two [Member] \| Restricted Stock Plan [Member]
Restricted Stock Activity
Share based compensation expense	1,960
Year three [Member] \| Restricted Stock Plan [Member]
Restricted Stock Activity
Share based compensation expense	1,211
Year four [Member] \| Restricted Stock Plan [Member]
Restricted Stock Activity
Share based compensation expense	731
Year five [Member] \| Restricted Stock Plan [Member]
Restricted Stock Activity
Share based compensation expense	439
Year six and thereafter [Member] \| Restricted Stock Plan [Member]
Restricted Stock Activity
Share based compensation expense	596
Salaries and Benefits \| Restricted Stock Plan [Member]
Restricted Stock Activity
Allocated share-based compensation expense	$ 4,200	$ 4,100	$ 5,200