Derivative Instruments - Hedge Derivatives (Details) - USD ($)		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Derivative [Line Items]
Closed Portfolio and Beneficial Interest, Last-of-Layer, Amortized Cost		$ 2,700,000,000	$ 2,700,000,000
Not Designated as Hedging Instrument
Derivative [Line Items]
Description of Location of Gain (Loss) on Interest Rate Derivative on Income Statement		Other noninterest income
Derivative, Gain (Loss) on Derivative, Net		$ (13,000)	(20,000)
Hedging derivative | Cash flow hedge
Derivative [Line Items]
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)		$ (523,000)	1,720,000
Hedging derivative | Fair value hedge
Derivative [Line Items]
Weighted Average Remaining Maturity		4 years 3 months 4 days
Pay Rate (as percent)		2.88%
Forecasted Notional Amount		$ 1,377,905,000		$ 1,377,905,000
Fair Value Hedge Assets		$ (36,967,000)		(21,833,000)
Hedging derivative | Fair value hedge | Loans
Derivative [Line Items]
Weighted Average Remaining Maturity		2 years 4 months 21 days
Pay Rate (as percent)		2.77%
Receive Rate		3 month LIBOR
Forecasted Notional Amount		$ 900,000,000		900,000,000
Fair Value Hedge Assets		(11,891,000)		(7,037,000)
Derivative Instruments and Hedges, Assets	[1]	911,891,000		907,037,000
Fair Value Hedging Adjustment	[1]	$ 11,891,000		7,037,000
Description of Location of Gain (Loss) on Interest Rate Derivative on Income Statement		Interest income on loans
Description of Location of Interest Rate Fair Value Hedge Derivative on Balance Sheet		Other liabilities
Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge		$ 4,854,000	0
Gain (Loss) on Fair Value Hedges Recognized in Earnings		$ (4,854,000)	0
Hedging derivative | Fair value hedge | Securities
Derivative [Line Items]
Weighted Average Remaining Maturity		7 years 9 months 18 days
Pay Rate (as percent)		3.08%
Receive Rate		3 month LIBOR
Forecasted Notional Amount		$ 477,905,000		477,905,000
Fair Value Hedge Assets		(25,076,000)		(14,796,000)
Derivative Instruments and Hedges, Assets		528,900,000		513,116,000
Fair Value Hedging Adjustment		$ 25,076,000		14,796,000
Description of Location of Gain (Loss) on Interest Rate Derivative on Income Statement		Interest income on securities
Description of Location of Interest Rate Fair Value Hedge Derivative on Balance Sheet		Other liabilities
Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge		$ 10,280,000	(1,579,000)
Gain (Loss) on Fair Value Hedges Recognized in Earnings		$ (10,280,000)	$ 1,579,000
Liability derivatives | Hedging derivative | Cash flow hedge
Derivative [Line Items]
Description of Location of Interest Rate Derivatives on Balance Sheet		Other liabilities
Weighted Average Remaining Maturity		3 years 1 month 6 days
Pay Rate (as percent)		3.09%
Receive Rate		3 month LIBOR
Forecasted Notional Amount		$ 99,000,000		99,000,000
Cash Flow Hedges Derivative Instruments at Fair Value, Net		$ (2,466,000)		$ (1,757,000)

[1] The carrying amount as shown represents the designated last-of-layer. At March 31, 2019 and December 31, 2018, the total amortized cost basis of the closed portfolio of loans designated in these hedging relationships was $2.7 billion.