Investments - Amortized cost and estimated fair value of investments in available-for-sale securities, by contractual maturity (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014
Cost
Mature after one year through three years	$ 223
Mature in more than three years	31,025
Total debt securities	31,248
Securities with no contractual maturities	164,208
Total	195,456
Estimated Fair Value
Mature after one year through three years	228
Mature in more than three years	31,852
Total debt securities	32,080
Securities with no contractual maturities	180,109
Total	$ 212,189