Acquisition (Details) $ / shares in Units, $ in Thousands, shares in Millions			3 Months Ended		9 Months Ended
	Aug. 21, 2019 $ / shares	Jan. 31, 2019 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares	Sep. 30, 2018 USD ($) $ / shares	Sep. 30, 2019 USD ($) $ / shares	Sep. 30, 2018 USD ($) $ / shares	Dec. 31, 2018 USD ($)
Merger agreement
Decrease to other liabilities					$ (3,603)	$ (5,366)
Consideration paid
Goodwill			$ 322,699		322,699		$ 267,685
Banc Ed
Merger agreement
Share consideration conversion ratio	8.2067
Per share cash consideration entitled (in dollars per share) | $ / shares	$ 111.53
Number of common shares issued for acquisition | shares		6.7
Market value of common stock issued		$ 166,500
Common stock		$ 166,515
Share price | $ / shares		$ 24.76
Decrease to premises and equipment			(100)
Decrease to other liabilities			(300)
Decrease to goodwill			(200)
Assets acquired:
Cash and cash equivalents		$ 42,013
Securities		692,716
Loans held for sale		2,157
Portfolio loans		873,336
Premises and equipment		31,804
Other intangible assets		32,617
Mortgage servicing rights		6,946
Other assets		57,296
Total assets acquired		1,738,885
Liabilities assumed:
Deposits		1,439,203
Other borrowings		63,439
Other liabilities		24,760
Total liabilities assumed		1,527,402
Net assets acquired		211,483
Consideration paid
Cash		91,400
Common stock		166,515
Total consideration paid		257,915
Goodwill		46,432
Aggregate principal outstanding		889,300
Fair value of performing loans, including loans held for sale		871,000
Amount expected to be accreted, gross		17,000
Contractual amount of PCI loans		3,900
Accretable discount on PCI loans		200
Fair value of credit-impaired loans		$ 2,300	1,500		1,500
Total revenues (net interest income plus non-interest income)					53,700
Net income					9,500
Banc Ed | Pro Forma
Consideration paid
Total revenues (net interest income plus non-interest income)			104,543,000	$ 101,001,000	305,709,000	306,472,000
Net income			$ 30,811,000	$ 31,641,000	$ 84,742,000	$ 87,972,000
Diluted earnings per common share (in dollars per share) | $ / shares			$ 0.55	$ 0.57	$ 1.51	$ 1.60
Banc Ed | Non-interest expense
Merger agreement
Business acquisition expenses			$ 6,500		$ 11,500
IST | Non-interest expense
Merger agreement
Business acquisition expenses			$ 500		$ 700