Assets and Liabilities Measured at Fair Value - Fair values for other financial instruments that are not measured at fair value on recurring basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Securities held-to-maturity	$ 413,820	$ 287,904
Carrying Amount
Assets:
Securities held-to-maturity	398,373	283,533
Loans and leases, net	11,664,654	8,750,464
Liabilities:
Deposits	14,603,376	10,897,244
Long-term debt	326,703	212,664
Fair Value
Assets:
Securities held-to-maturity	413,820	287,904
Loans and leases, net	11,651,643	8,714,592
Liabilities:
Deposits	14,604,902	10,897,465
Long-term debt	332,869	217,665
Fair Value | Level 1
Assets:
Securities held-to-maturity	0	0
Loans and leases, net	0	0
Liabilities:
Deposits	0	0
Long-term debt	0	0
Fair Value | Level 2
Assets:
Securities held-to-maturity	413,820	287,904
Loans and leases, net	0	0
Liabilities:
Deposits	14,604,902	10,897,465
Long-term debt	0	0
Fair Value | Level 3
Assets:
Securities held-to-maturity	0	0
Loans and leases, net	11,651,643	8,714,592
Liabilities:
Deposits	0	0
Long-term debt	$ 332,869	$ 217,665