Note 8 - Earnings Per Share Reconciliation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Common Class A [Member] | Employee Stock Option [Member]
Shares issuable pursuant to stock options not included since they were antidilutive (in shares)	20	15
Common Class A [Member] | Distributed [Member]
Reallocation of distributed net income as a result of conversion of dilutive stock options	$ 3	$ 4
Reallocation of distributed net income due to conversion of Class B to Class A common shares outstanding	455	407
Common Class A [Member] | Diluted [Member]
Distributed net income applicable to common stockholders	(5,151)	(4,216)
Distributed net income applicable to common stockholders	5,151	4,216
Common Class A [Member] | Undistributed [Member]
Reallocation of distributed net income as a result of conversion of dilutive stock options	18	32
Reallocation of distributed net income due to conversion of Class B to Class A common shares outstanding	3,102	3,520
Diluted undistributed net income applicable to common stockholders	35,119	36,437
Common Class A [Member]
Net income applicable to common stockholders	36,692	36,690
Distributed net income applicable to common stockholders	(4,693)	(3,805)
Basic undistributed net income applicable to common stockholders	$ 31,999	$ 32,885
Weighted average number of shares outstanding used to calculate basic net income per share (in shares)	23,522	23,721
Basic net income per share applicable to common stockholders (in dollars per share)	$ 1.56	$ 1.55
Basic distributed net income per share applicable to common stockholders (in dollars per share)	(0.20)	(0.16)
Basic undistributed net income per share applicable to common stockholders (in dollars per share)	$ 1.36	$ 1.39
Distributed net income applicable to common stockholders	$ 4,693	$ 3,805
Weighted average number of shares from stock options (in shares)	157	236
Conversion of Class B to Class A common shares outstanding (in shares)	2,294	2,562
Weighted average number of shares outstanding used to calculate diluted net income per share (in shares)	25,973	26,519
Diluted net income per share applicable to common stockholders (in dollars per share)	$ 1.55	$ 1.53
Diluted distributed net income per share applicable to common stockholders (in dollars per share)	(0.20)	(0.16)
Diluted undistributed net income per share applicable to common stockholders (in dollars per share)	$ 1.35	$ 1.37
Common Class B [Member] | Distributed [Member]
Reallocation of distributed net income as a result of conversion of dilutive stock options	$ (3)	$ (4)
Reallocation of distributed net income due to conversion of Class B to Class A common shares outstanding
Common Class B [Member] | Diluted [Member]
Distributed net income applicable to common stockholders	$ (455)	$ (407)
Distributed net income applicable to common stockholders	455	407
Common Class B [Member] | Undistributed [Member]
Reallocation of distributed net income as a result of conversion of dilutive stock options	(18)	(32)
Diluted undistributed net income applicable to common stockholders	3,102	3,520
Common Class B [Member]
Net income applicable to common stockholders	3,578	3,963
Distributed net income applicable to common stockholders	(458)	(411)
Basic undistributed net income applicable to common stockholders	$ 3,120	$ 3,552
Weighted average number of shares outstanding used to calculate basic net income per share (in shares)	2,294	2,562
Basic net income per share applicable to common stockholders (in dollars per share)	$ 1.56	$ 1.55
Basic distributed net income per share applicable to common stockholders (in dollars per share)	(0.20)	(0.16)
Basic undistributed net income per share applicable to common stockholders (in dollars per share)	$ 1.36	$ 1.39
Distributed net income applicable to common stockholders	$ 458	$ 411
Weighted average number of shares from stock options (in shares)
Conversion of Class B to Class A common shares outstanding (in shares)
Weighted average number of shares outstanding used to calculate diluted net income per share (in shares)	2,294	2,562
Diluted net income per share applicable to common stockholders (in dollars per share)	$ 1.55	$ 1.53
Diluted distributed net income per share applicable to common stockholders (in dollars per share)	(0.20)	(0.16)
Diluted undistributed net income per share applicable to common stockholders (in dollars per share)	$ 1.35	$ 1.37
Weighted average number of shares outstanding used to calculate basic net income per share (in shares)	25,816	26,283
Weighted average number of shares outstanding used to calculate diluted net income per share (in shares)	25,973	26,519
Diluted net income per share applicable to common stockholders (in dollars per share)	$ 1.55	$ 1.53