Note 10 - Capital Resources - Outstanding Junior Subordinated Notes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	May 31, 2014
Junior subordinated debt	$ 119,136,000	$ 119,100,000
Cathay Capital Trust I [Member]
Issuance date	Jun. 26, 2003
Junior subordinated debt	$ 20,619,000
Not redeemable until	Jun. 30, 2008
Stated maturity	Jun. 30, 2033
Annualized coupon rate	3-month LIBOR + 3.15%
Current interest rate	4.84%
Date of rate change	Dec. 30, 2017
Payable/distribution date	March 30, June 30, September 30, December 30
Cathay Statutory Trust I [Member]
Issuance date	Sep. 17, 2003
Junior subordinated debt	$ 20,619,000
Not redeemable until	Sep. 17, 2008
Stated maturity	Sep. 17, 2033
Annualized coupon rate	3-month LIBOR + 3.00%
Current interest rate	4.60%
Date of rate change	Dec. 18, 2017
Payable/distribution date	March 17, June 17, September 17, December 17
Cathay Capital Trust II [Member]
Issuance date	Dec. 30, 2003
Junior subordinated debt	$ 12,887,000
Not redeemable until	Mar. 30, 2009
Stated maturity	Mar. 30, 2034
Annualized coupon rate	3-month LIBOR + 2.90%
Current interest rate	4.59%
Date of rate change	Dec. 30, 2017
Payable/distribution date	March 30, June 30, September 30, December 30
Cathay Capital Trust III [Member]
Issuance date	Mar. 28, 2007
Junior subordinated debt	$ 46,392,000
Not redeemable until	Jun. 15, 2012
Stated maturity	Jun. 15, 2037
Annualized coupon rate	3-month LIBOR + 1.48%
Current interest rate	3.07%
Date of rate change	Dec. 15, 2017
Payable/distribution date	March 15, June 15, September 15, December 15
Cathay Capital Trust IV [Member]
Issuance date	May 31, 2007
Junior subordinated debt	$ 18,619,000
Not redeemable until	Sep. 06, 2012
Stated maturity	Sep. 06, 2037
Annualized coupon rate	3-month LIBOR + 1.4%
Current interest rate	2.91%
Date of rate change	Dec. 06, 2017
Payable/distribution date	March 6, June 6, September 6, December 6