Debt Securities Available for Sale - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($) security	Dec. 31, 2019 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 1,132,936,000		$ 1,132,936,000		$ 1,086,143,000
Debt securities available for sale, at fair value	1,177,925,000		1,177,925,000		1,098,336,000
Proceeds from sales of debt securities available for sale	0	$ 15,700,000	20,761,000	$ 15,711,000
Proceeds from calls of debt securities available for sale	5,500,000	0	6,600,000	797,000
Gross gains or losses on debt securities available-for-sale	0
Sale and maturity of debt securities, available-for-sale	5,100,000	0	5,800,000	0
Gross gains on sale of available-for-sale securities		339,000	369,000	339,000
Gross losses on sale of available-for-sale securities		0	0	$ 0
Calls of debt securities, available-for-sale, realized gain			1,000
Calls of debt securities, available-for-sale, unrealized loss			0
Number of debt securities called | security				1
Debt securities, available-for-sale, gain (loss)				$ 0
Debt securities, available-for-sale, restricted	$ 769,700,000		$ 769,700,000		$ 462,000,000.0
Number of securities in unrealized loss position | security	31		31		97
Other-than-temporary impairments charge on debt securities available for sale	$ 0	$ 0	$ 0	$ 0
Mortgage-backed securities and collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Amortized cost	1,013,079,000		1,013,079,000		$ 968,165,000
Debt securities available for sale, at fair value	$ 1,056,228,000		$ 1,056,228,000		$ 979,881,000