Marketable Securities (Details 1) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Schedule of Amortized Cost and Estimated Fair Value of Debt Securities
Due in one year or less, Amortized Cost	$ 79,382
Due after one year through three years, Amortized Cost	209,185
Due after three years through five years, Amortized Cost	42,618
Due after five years, Amortized Cost	47,131
Total amortized cost of debt securities	378,316
Due in one year or less, Estimated Fair Value	79,461
Due after one year through three years, Estimated Fair Value	210,535
Due after three years through five years, Estimated Fair Value	43,016
Due after five years, Estimated Fair Value	47,939
Total estimated fair value of debt securities	$ 380,951