Derivative Instruments and Balance Sheet Offsetting - Notional Amount and Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Derivative instruments
Notional Amount	$ 3,694,987	$ 3,516,418
Gross Derivative Assets	47,359	38,595
Gross Derivative Liabilities	49,498	32,379
Credit valuation adjustments for counterparty credit risk	1,200	900
Derivatives designated as hedging instruments:
Derivative instruments
Notional Amount	820,000	820,000
Gross Derivative Assets	5,322	10,148
Gross Derivative Liabilities	7,292	3,278
Derivatives designated as hedging instruments: \| Interest rate swaps
Derivative instruments
Notional Amount	820,000	820,000
Gross Derivative Assets	5,322	10,148
Gross Derivative Liabilities	7,292	3,278
Derivatives not designated as hedging \| Total customer-initiated and mortgage banking derivatives
Derivative instruments
Notional Amount	2,874,987	2,696,418
Gross Derivative Assets	42,037	28,447
Gross Derivative Liabilities	42,206	29,101
Derivatives not designated as hedging \| Customer-initiated derivatives
Derivative instruments
Notional Amount	2,635,769	2,477,640
Gross Derivative Assets	39,398	26,680
Gross Derivative Liabilities	40,672	27,664
Derivatives not designated as hedging \| Forward contracts related to mortgage loans to be delivered for sale
Derivative instruments
Notional Amount	110,328	127,159
Gross Derivative Assets	0	0
Gross Derivative Liabilities	653	719
Derivatives not designated as hedging \| Interest rate lock commitments
Derivative instruments
Notional Amount	92,684	54,848
Gross Derivative Assets	1,758	1,049
Gross Derivative Liabilities	0	0
Derivatives not designated as hedging \| Power Equity CD
Derivative instruments
Notional Amount	36,206	36,771
Gross Derivative Assets	881	718
Gross Derivative Liabilities	$ 881	$ 718

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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