Marketable Securities - Maturities of Held to Maturity Investments (Details) $ in Thousands	Sep. 30, 2015 USD ($)
Marketable Securities [Abstract]
Held-to-maturity investments, maturities due within one year	$ 17,607
Held-to-maturity investments, maturities due in one to five years	70,646
Held-to-maturity investments, total maturities due	$ 88,253