Derivative Financial Instruments and Hedging - Table of Derivatives - Gross notional and fair value amounts of derivatives (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional values	$ 376,049	$ 458,797
Asset derivatives	4,820	5,013
Liability derivatives	77	117
Interest Risk, Interest Rate Lock Commitments
Derivative [Line Items]
Notional values	173,114	190,645
Asset derivatives	4,393	4,808
Liability derivatives	0	0
Interest Risk, Forward Delivery Contracts
Derivative [Line Items]
Notional values	34,935	71,152
Asset derivatives	16	30
Liability derivatives	0	0
Interest Risk, TBA Mortgage Backed Securities
Derivative [Line Items]
Notional values	168,000	197,000
Asset derivatives	411	175
Liability derivatives	$ 77	$ 117