Preparation of Interim Financial Statements (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) financial_center	Jan. 01, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Number of financial centers | financial_center	191
Unrealized gain on AFS securities	$ 2,547
Operating lease, right-of-use asset	30,500
Operating lease, liability	30,400
Accounting Standards Update 2017-12
Lessee, Lease, Description [Line Items]
Fair value of HTM municipal bonds	216,400
Unrealized gain on AFS securities	$ 2,500
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease, right-of-use asset		$ 32,800
Operating lease, liability		$ 32,800