Derivative Instruments and Balance Sheet Offsetting - Notional Amount and Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Derivative instruments
Notional Amount	$ 1,910,279	$ 853,594
Gross Derivative Assets	14,713	8,215
Gross Derivative Liabilities	11,739	6,359
Credit valuation adjustments for counterparty credit risk	576	99
Derivatives designated as hedging instruments:
Derivative instruments
Notional Amount	520,000	0
Gross Derivative Assets	1,174	0
Gross Derivative Liabilities	109	0
Derivatives designated as hedging instruments: | Interest rate swaps
Derivative instruments
Notional Amount	520,000	0
Gross Derivative Assets	1,174	0
Gross Derivative Liabilities	109	0
Derivatives not designated as hedging | Total customer-initiated and mortgage banking derivatives
Derivative instruments
Notional Amount	1,390,279	853,594
Gross Derivative Assets	13,539	8,215
Gross Derivative Liabilities	11,630	6,359
Derivatives not designated as hedging | Customer-initiated derivatives
Derivative instruments
Notional Amount	1,059,921	600,598
Gross Derivative Assets	8,719	4,406
Gross Derivative Liabilities	9,274	4,141
Derivatives not designated as hedging | Foreign exchange forwards
Derivative instruments
Notional Amount	4,000	0
Gross Derivative Assets	60	0
Gross Derivative Liabilities	55	0
Derivatives not designated as hedging | Forward contracts related to mortgage loans to be delivered for sale
Derivative instruments
Notional Amount	180,961	140,155
Gross Derivative Assets	660	635
Gross Derivative Liabilities	0	0
Derivatives not designated as hedging | Interest rate lock commitments
Derivative instruments
Notional Amount	106,649	76,034
Gross Derivative Assets	1,799	956
Gross Derivative Liabilities	0	0
Derivatives not designated as hedging | Power Equity CD
Derivative instruments
Notional Amount	38,748	36,807
Gross Derivative Assets	2,301	2,218
Gross Derivative Liabilities	$ 2,301	$ 2,218