Loans and Loans Held for Sale - Additional Information (Details) $ in Thousands				3 Months Ended			12 Months Ended
		Mar. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($)	Mar. 31, 2020 USD ($) note loan		Mar. 31, 2019 USD ($) loan	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income		$ 5,000	$ 4,600	$ 5,000			$ 4,600
Purchase accounting fair value adjustments		$ 10,900	$ 12,300
Threshold period of satisfactory performance for troubled debt restructuring to be restored to accruing status				6 months
Restructured loans	[1]			$ 8,297	[2]	$ 5,499
Number of troubled debt restructuring loans returned to accruing status | loan				0		3
Amount of trouble debt restructuring loans returned to accruing status						$ 1,700
Number of commitments to lend additional funds on TDRs | loan		20		20
Commitments to lend additional funds on TDRs		$ 2,300		$ 2,300
Minimum period of loan payment defaults following restructure for TDRs to be in default				90 days
Number of defaulted TDRs that were restructured within the last twelve months prior to defaulting | loan				11		0
Amount of defaulted TDRs that were restructured within the last twelve months prior to defaulting				$ 21,100
Number of notes related to individual customer resulting in an increase in defaulted troubled debt restructuring loans due to Covid-19 | note				5
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of commercial loans in total portfolio loans		77.60%	77.20%	77.60%			77.20%
Commercial loans			$ 5,512,796				$ 5,512,796
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restructured loans	[1]			$ 2,210
Commercial real estate | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans			3,416,518				3,416,518
CRE and commercial construction | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans		$ 3,800,000	$ 3,800,000	$ 3,800,000			$ 3,800,000
Combined percentage of commercial real estate and commercial construction in total commercial loans		68.30%	68.80%	68.30%			68.80%
Combined percentage of commercial real estate and commercial construction in total portfolio loans		53.00%	53.10%	53.00%			53.10%
Concentration risk percentage of commercial real estate and commercial construction				0.00%			0.00%
Maximum concentration of commercial real estate and commercial construction portfolio in loans (in excess of)		13.60%	11.00%	13.60%			11.00%
Out of market exposure of combined portfolio (percent)		5.40%	5.40%	5.40%			5.40%
Percentage of total loans out-of-state excluding contiguous states		2.80%	2.90%	2.80%			2.90%
Nonperforming TDRs | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restructured loans				$ 20,900

[1] Excludes loans that were fully paid off or fully charged-off by period end. The pre-modification balance represents the balance outstanding prior to modification. The post-modification balance represents the outstanding balance at period end.

[2] Refer to Note 1, Basis of Presentation for details of reclassification of our portfolio segments related to the adoption of ASU 2016-13 Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instrument.