Equity Incentive Plan - Restricted share activity (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted	0	0	0
Omnibus Incentive Plan2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of Common stock			700,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Outstanding, Unvested restricted stock at beginning of the period	227,000	228,000	213,000
Shares Outstanding, Restricted stock granted	57,247	88,466	93,363
Shares Outstanding, Restricted stock vested	(72,000)	(78,000)	(72,000)
Shares Outstanding, Restricted stock forfeited	(1,000)	(11,000)	(6,000)
Shares Outstanding, Unvested restricted stock at end of the period	211,000	227,000	228,000
Weighted Average Grant Date Fair Value, Unvested restricted stock at beginning of the period (in dollars per share)	$ 39.47	$ 33.02	$ 29.07
Weighted Average Grant Date Fair Value, Restricted stock granted (in dollars per share)	48.85	48.59	37.67
Weighted Average Grant Date Fair Value, Restricted stock vested (in dollars per share)	36.06	30.95	27.07
Weighted Average Grant Date Fair Value, Restricted stock forfeited (in dollars per share)	48.28	39.68	35.58
Weighted Average Grant Date Fair Value, Unvested restricted stock at end of the period (in dollars per share)	$ 43.15	$ 39.47	$ 33.02

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Paragraph 2
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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).

+ References

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The weighted average fair value at grant date for nonvested equity-based awards issued 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).

+ References

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-Publisher FASB
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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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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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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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-Publisher FASB
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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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-Publisher FASB
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- Definition

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 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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-Publisher FASB
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Gross number of share options (or share units) granted during the period.

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