Fair Value Measurements and Derivative Instruments (Available-for-sale Securities Maturities) (Details) $ in Thousands	Sep. 30, 2017 USD ($)
Amortized cost
Within 1 year	$ 42,982
After 1 year through 5 years	109,866
After 5 years through 10 years	61,744
After 10 years	158,387
Total	372,979
Estimated fair value
Within 1 year	42,865
After 1 year through 5 years	110,445
After 5 years through 10 years	62,673
After 10 years	160,317
Total	$ 376,300