Note 7 - Stock-Based Compensation (Detail) - Restricted Stock Awards Activity (USD $)								12 Months Ended
	Dec. 31, 2011	Dec. 31, 2011 Restricted Stock [Member] Beginning Of Period [Member]		Dec. 31, 2010 Restricted Stock [Member] Beginning Of Period [Member]		Dec. 31, 2011 Restricted Stock [Member] End Of Period [Member]		Dec. 31, 2012 Restricted Stock [Member]		Dec. 31, 2011 Restricted Stock [Member]
Outstanding shares	179,710			400,900	[1]	477,354	[1],[2]
Outstanding - weighted average remaining vesting period						2 years 219 days	[1],[2]	1 year 292 days	[1],[2]
Outstanding - weighted average fair value (in Dollars per share)		$ 30.80	[1]			$ 34.40	[1],[2]	$ 39.44	[1],[2]
Issued shares								268,840		311,600
Issued - weighted average remaining vesting period								3 years
Issued - weighted average fair value (in Dollars per share)								$ 40.08		$ 39.48
Forfeited shares								(28,829)		(25,784)
Forfeited - weighted average remaining vesting period								2 years
Forfeited - weighted average fair value (in Dollars per share)								$ 39.07		$ 36.22
Vested shares								(214,274)		(209,362)
Vested - weighted average remaining vesting period								0 years
Vested - weighted average fair value (in Dollars per share)								$ 36.45		$ 34.68
Outstanding shares	179,710			400,900	[1]	477,354	[1],[2]	503,091	[1],[2]

[1] Subject to restriction.

[2] Includes 82,222 restricted shares with nonforfeitable dividend rights.