Fair Value Measurements and Derivative Instruments (Available-for-sale Securities Maturities) (Details) $ in Thousands	Jun. 30, 2017 USD ($)
Amortized cost
Within 1 year	$ 24,079
After 1 year through 5 years	116,356
After 5 years through 10 years	65,193
After 10 years	157,559
Total	363,187
Estimated fair value
Within 1 year	24,146
After 1 year through 5 years	116,910
After 5 years through 10 years	65,864
After 10 years	159,174
Total	$ 366,094