Note 9 - Employee Benefit Program (Details Textual) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2018
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount	$ 18,500	$ 18,500	$ 18,000
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	4.50%	4.50%	4.50%
Defined Contribution Plan, Cost	$ 470,000	$ 486,000	$ 508,000
BTC [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	4.50%	4.50%	4.50%
Defined Contribution Plan, Cost	$ 21,000	$ 16,000	$ 16,000
Defined Contribution Plan, Minimum Annual Contributions Per Employee, Percent	1.00%
Multiemployer Plan, Contributions by Employer	$ 0	$ 0	$ 0
RSP [Member]
Multiemployer Plans, Collective-Bargaining Arrangement, Percentage of Employer's Participants	0.30%
Multiemployer Plans, Collective-Bargaining Arrangement, Percentage of Participants	0.10%
Defined Benefit Plan, Funded Percentage		98.00%
Multiemployer Plans, Plan Assets				$ 2,400,000,000

Minimum percentage of employee gross pay the employee required to contribute to a defined contribution plan.

No definition available.

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- Definition

Percentage of plan assets to benefit obligation of defined benefit plan.

+ References

No definition available.

+ Details

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- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

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- Definition

Maximum amount the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

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- Definition

Amount of contributions made to multiemployer plan by employer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 80
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947

+ Details

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- Definition

Percentage of employee participants subject to a collective bargaining arrangement to all of the employer's participants in a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947

+ Details

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- Definition

Percentage of employee participants subject to a collective bargaining arrangement to all participants in a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

+ Details

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- Definition

Amount of plan assets attributable to the pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 7
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450678-114947

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