Acquisitions (Details) $ / shares in Units, $ in Thousands, shares in Millions		3 Months Ended		9 Months Ended
	Aug. 23, 2018 USD ($) $ / shares shares	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Total assets		$ 5,627,057		$ 5,627,057			$ 5,405,639
Loans, net of deferred costs (fees)		4,328,118		4,328,118			4,152,720
Total loans		4,290,825		4,290,825			4,117,265
Total deposits		4,642,443		4,642,443			4,368,748
Total stockholders' equity		607,555	$ 577,081	607,555	$ 577,081	$ 597,864	$ 583,122	$ 567,545	$ 550,044
Net income		16,758	$ 13,723	47,851	$ 39,405
Highlands Bancorp, Inc. Acquisition
Business Acquisition [Line Items]
Share conversion ratio	1.015
Number of shares issued | shares	2.8
Shares issued	$ 56,700
Shares issued (in dollars per share) | $ / shares	$ 19.79
Highlands Bancorp
Business Acquisition [Line Items]
Total assets		487,900		487,900
Loans, net of deferred costs (fees)		430,100		430,100
Total deposits		405,300		405,300
Total stockholders' equity		$ 31,300		31,300
Net income				$ 2,700