Investment Securities - Maturity (Details) $ in Thousands	Jun. 30, 2017 USD ($)
Amortized Cost
Within one year	$ 24,008
After one year but within five years	20,140
After 10 years	5,000
Total amortized cost	49,148
Fair value
Within one year	24,007
After one year but within five years	20,126
After 10 years	5,000
Total fair value	49,133
Fair value
Within one year	6,014
After one year but within five years	10,089
After five years but within 10 years	7
Total fair value	$ 16,110