Derivative Instruments - Summary of contingent credit features (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Collateral posted to counterparty	[1]	$ 8,260	$ 0
Contracts with downgrade provisions [Member]
Derivative [Line Items]
Aggregate fair value of derivative agreements with downgrade provisions in a net liability position		$ 6,186	$ 5,827

[1] Derivative instruments in an asset or liability position are included within Other assets or Other liabilities, respectively, in the balance sheets on a net basis where the Company has both a legal right of offset and the intention to settle the contracts on a net basis. The Company often enters into different types of derivative contracts with a single counterparty and these contracts are covered under netting agreements.