Note 11 - Equity-based Compensation - Deferred Stock Unit Activity (Details) - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock Awards, Outstanding (in shares)	1,143,205	1,428,878	1,501,021
Weighted average award date fair value (in dollars per share)	$ 23.26	$ 21.53	$ 20.58
Stock Awards, Outstanding (in shares)	1,034,964	1,143,205	1,428,878
Weighted average award date fair value (in dollars per share)	$ 23.20	$ 23.26	$ 21.53
Deferred Stock Units [Member]
Stock Awards, Outstanding (in shares)	287,350	269,977	253,445
Weighted average award date fair value (in dollars per share)	$ 20.80	$ 20.14	$ 19.93
Awards, grants during period (in shares)	50,174	45,681	47,091
Weighted average award date fair value, award granted (in dollars per share)	$ 19.64	$ 23.72	$ 23.53
Awards, distributed during period (in shares)	(84,184)	(28,308)	(30,559)
Weighted average award date fair value, award distributed (in dollars per share)	$ 20.38	$ 19.22	$ 23.57
Stock Awards, Outstanding (in shares)	253,340	287,350	269,977
Weighted average award date fair value (in dollars per share)	$ 20.71	$ 20.80	$ 20.14

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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-Subparagraph (c)(2)(iii)(1)
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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).

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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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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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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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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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