Cash, Cash Equivalents and Investments (Summary Of Cash, Cash Equivalents And Available-For-Sale Investments) (Details) - USD ($) $ in Thousands	Aug. 31, 2017	Nov. 30, 2016
Cash, Cash Equivalents and Investments [Line Items]
Amortized Cost Basis	$ 191,289	$ 249,894
Unrealized Gains	45	0
Unrealized Losses	(18)	(140)
Fair Value	191,316	249,754
State and municipal bond obligations [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized Cost Basis	37,690	32,831
Unrealized Gains	45	0
Unrealized Losses	0	(107)
Fair Value	37,735	32,724
U.S. treasury bonds [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized Cost Basis	3,523	6,542
Unrealized Gains	0	0
Unrealized Losses	(17)	(29)
Fair Value	3,506	6,513
Corporate bonds [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized Cost Basis	6,319	3,485
Unrealized Gains	0	0
Unrealized Losses	(1)	(4)
Fair Value	6,318	3,481
Cash [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized Cost Basis	137,911	196,863
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	137,911	196,863
Money market funds [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized Cost Basis	5,846	10,173
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	$ 5,846	$ 10,173