Securities - Contractual Maturities of Securities (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Available-for-sale, Amortized Cost
Due in one year or less	$ 1,787,000		$ 1,787,000
Due after one year through five years	102,239,000		102,239,000
Due after ten years	236,000		236,000
Total	104,262,000		104,262,000
Available-for-sale, Amortized Cost	688,229,000		688,229,000		$ 275,734,000
Available-for-sale, Fair Value
Due in one year or less	1,794,000		1,794,000
Due after one year through five years	102,583,000		102,583,000
Due after five years through ten years	243,000		243,000
Total	104,620,000		104,620,000
Available-for-sale Securities, Total	687,100,000		687,100,000		274,619,000
Held-to-maturity, Amortized Cost
Held-to-maturity, Amortized Cost	31,650,000		31,650,000		35,505,000
Held-to-maturity, Fair Value
Held-to-maturity, Fair Value	31,235,000		31,235,000		34,844,000
Proceeds from sale of securities
Proceeds from Sale and Maturity of Marketable Securities		$ 0	279,200,000	$ 0
Gain (loss) on sale of available-for-sale securities, net	294,000		294,000
Gross realized gains			777,000
Gross realized losses			483,000
Impairment loss realized in consolidated statements of income	0		0
Mortgage-backed securities and collateralized mortgage obligations
Available-for-sale, Amortized Cost
Amortized cost	572,669,000		572,669,000
Available-for-sale, Fair Value
Fair value	571,418,000		571,418,000
Held-to-maturity, Amortized Cost
Debt maturities without single maturity date	31,650,000		31,650,000
Held-to-maturity, Fair Value
Debt maturities without single maturity date	31,235,000		31,235,000
CRA qualified investment fund
Available-for-sale, Amortized Cost
Amortized cost	11,298,000		11,298,000
Available-for-sale, Amortized Cost	11,298,000		11,298,000		11,183,000
Available-for-sale, Fair Value
Fair value	11,062,000		11,062,000
Available-for-sale Securities, Total	$ 11,062,000		$ 11,062,000		$ 10,913,000