Derivative Instruments and Balance Sheet Offsetting - Notional Amount and Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Derivative instruments
Notional Amount	$ 1,783,085	$ 853,594
Gross Derivative Assets	13,536	8,215
Gross Derivative Liabilities	11,496	6,359
Credit valuation adjustments for counterparty credit risk	538	99
Derivatives designated as hedging instruments:
Derivative instruments
Notional Amount	400,000	0
Gross Derivative Assets	224	0
Gross Derivative Liabilities	282	0
Derivatives designated as hedging instruments: | Interest rate swaps
Derivative instruments
Notional Amount	400,000	0
Gross Derivative Assets	224	0
Gross Derivative Liabilities	282	0
Derivatives not designated as hedging | Total customer-initiated and mortgage banking derivatives
Derivative instruments
Notional Amount	1,383,085	853,594
Gross Derivative Assets	13,312	8,215
Gross Derivative Liabilities	11,214	6,359
Derivatives not designated as hedging | Customer-initiated derivatives
Derivative instruments
Notional Amount	1,055,917	600,598
Gross Derivative Assets	8,636	4,406
Gross Derivative Liabilities	9,152	4,141
Derivatives not designated as hedging | Forward contracts related to mortgage loans to be delivered for sale
Derivative instruments
Notional Amount	168,533	140,155
Gross Derivative Assets	617	635
Gross Derivative Liabilities	0	0
Derivatives not designated as hedging | Interest rate lock commitments
Derivative instruments
Notional Amount	120,095	76,034
Gross Derivative Assets	1,997	956
Gross Derivative Liabilities	0	0
Derivatives not designated as hedging | Power Equity CD
Derivative instruments
Notional Amount	38,540	36,807
Gross Derivative Assets	2,062	2,218
Gross Derivative Liabilities	$ 2,062	$ 2,218