Securities Available for Sale - Maturities (Details) $ in Thousands	Mar. 31, 2016 USD ($)
Fair value
Within 1 year	$ 52,594
After 1 year through 5 years	231,706
After 5 years through 10 years	0
After 10 years	0
Total	284,300
Amortized cost
Within 1 year	52,648
After 1 year through 5 years	232,520
After 5 years through 10 years	0
After 10 years	0
Total	285,168
Corporate debt securities
Fair value
Within 1 year	48,374
After 1 year through 5 years	160,797
After 5 years through 10 years	0
After 10 years	0
Total	209,171
Asset-backed securities
Fair value
Within 1 year	1,221
After 1 year through 5 years	46,858
After 5 years through 10 years	0
After 10 years	0
Total	48,079
U.S. agency securities
Fair value
Within 1 year	0
After 1 year through 5 years	16,583
After 5 years through 10 years	0
After 10 years	0
Total	16,583
U.S. Treasury securities
Fair value
Within 1 year	1,000
After 1 year through 5 years	2,516
After 5 years through 10 years	0
After 10 years	0
Total	3,516
Other securities
Fair value
Within 1 year	1,999
After 1 year through 5 years	4,952
After 5 years through 10 years	0
After 10 years	0
Total	$ 6,951