QUARTERLY DATA -UNAUDITED (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
QUARTERLY DATA -UNAUDITED [Abstract]
Total revenues	$ 259,908		$ 267,182		$ 271,129		$ 259,317		$ 236,312		$ 242,025		$ 260,051		$ 244,724		$ 1,057,536		$ 983,112		$ 825,581
Total costs and expenses	245,911		249,129		256,434		245,964		223,567		226,496		243,143		231,161		997,438		924,367		786,007
Earnings before provision for income taxes	13,997		18,053		14,695		13,353		12,745		15,529		16,908		13,563		60,098		58,745		39,574
Provision for income taxes	5,775		7,443		6,104		5,503		5,043		6,496		6,875		5,501		24,825		23,915		16,207
Net earnings	$ 8,222		$ 10,610		$ 8,591		$ 7,850		$ 7,702		$ 9,033		$ 10,033		$ 8,062		$ 35,273		$ 34,830		$ 23,367
Net earnings per common share - Basic (in dollars per share)	$ 1.04	[1]	$ 1.33	[1]	$ 1.07	[1]	$ 0.98	[1]	$ 0.96	[1]	$ 1.11	[1]	$ 1.26	[1]	$ 1.01	[1]	$ 4.41		$ 4.37	[1]	$ 2.82
Net earnings per common share - Diluted (in dollars per share)	$ 1.03	[1]	$ 1.32	[1]	$ 1.06	[1]	$ 0.97	[1]	$ 0.95	[1]	$ 1.11	[1]	$ 1.25	[1]	$ 1.00	[1]	$ 4.37	[1]	$ 4.32	[1]	$ 2.79

[1] Basic and diluted earnings per share are computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share information may not equal annual basic and diluted earnings per share.