Financial Instruments and Off-Balance Sheet Risk Interest Rate Derivatives - Notional Amounts (Details) - Designated as Hedging Instrument - Cash Flow Hedging |
Dec. 31, 2016
USD ($)
|
|---|---|
| Interest Rate Swaps Ending January 2017 | |
| Derivative [Line Items] | |
| Notional amount | $ 250,000,000 |
| Interest Rate Swaps Ending April 2017 | |
| Derivative [Line Items] | |
| Notional amount | 25,000,000 |
| Interest Rate Swaps Ending January 2018 | |
| Derivative [Line Items] | |
| Notional amount | 225,000,000 |
| Interest Rate Swaps Ending January 2019 | |
| Derivative [Line Items] | |
| Notional amount | $ 200,000,000 |