Debt Securities Available for Sale - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($) security	Dec. 31, 2018 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 1,086,761,000		$ 1,086,761,000		$ 1,049,932,000
Debt securities available for sale, at fair value	1,099,801,000		1,099,801,000		1,032,868,000
Proceeds from sales of debt securities available for sale	15,700,000	$ 0	15,711,000	$ 0
Gross gains on sale of available-for-sale securities	339,000		339,000	116,000
Gross losses on sale of available-for-sale securities	$ 0		$ 0	$ 0
Number of debt securities called | security	0			1
Number of matured debt securities | security	1		1
Sale and maturity of debt securities, available-for-sale	$ 0		$ 797,000
Proceeds from calls of debt securities available for sale		0	0	$ 10,000,000
Debt securities, available-for-sale, restricted	$ 210,500,000		$ 210,500,000		$ 232,700,000
Number of securities in unrealized loss position | security	64		64		151
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	965,224,000		965,224,000		$ 934,631,000
Debt securities available for sale, at fair value	$ 978,419,000		$ 978,419,000		$ 920,007,000