Preparation of Interim Financial Statements (Details) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019 USD ($) financial_center	Mar. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) financial_center	Jun. 30, 2018 USD ($)	Jan. 01, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Number of financial centers | financial_center	212			212
Unrealized holding gain on the transfer of held-to-maturity securities to available-for-sale per ASU 2017-12	$ 0		$ 0	$ 2,547	$ 0
Right-of-use asset	35,200			35,200
Right-of-use liabilities	35,200			35,200
Accounting Standards Update 2018-15
Lessee, Lease, Description [Line Items]
Software implementation costs, not yet capitalized	$ 646			$ 646
Accounting Standards Update 2017-12
Lessee, Lease, Description [Line Items]
Fair value of HTM municipal bonds		$ 216,400
Unrealized holding gain on the transfer of held-to-maturity securities to available-for-sale per ASU 2017-12		$ 2,500
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Right-of-use asset						$ 32,800
Right-of-use liabilities						$ 32,800