Investments in debt and equity securities available-for-sale - Debt Securities According to Contractual Terms (Details) $ in Thousands	Mar. 31, 2017 USD ($)
Amortized costs
In one year or less	$ 41,967
After one year through five years	260,428
After five years through ten years	230,514
After ten years	77,375
Amortized costs, total	610,284
Fair values
In one year or less	42,258
After one year through five years	266,216
After five years through ten years	232,252
After ten years	78,773
Fair values, total	$ 619,499