Acquisitions - The Banc Ed Corp. (Details) $ / shares in Units, shares in Millions			3 Months Ended
	Aug. 21, 2019 $ / shares	Jan. 31, 2019 USD ($) $ / shares shares	Mar. 31, 2020 USD ($) $ / shares	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Consideration paid
Goodwill			$ 311,536,000		$ 311,536,000
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		$ 166,500,000
Common stock		$ 166,515,000
Share price | $ / shares		$ 24.76
Goodwill acquired		$ 41,400,000
Business acquisition expenses			0	$ 1,000,000.0
Assets acquired:
Cash and cash equivalents		42,013,000
Securities		692,716,000
Loans held for sale		2,157,000
Portfolio loans		873,336,000
Premises and equipment		32,156,000
Other intangible assets		32,617,000
Mortgage servicing rights		6,946,000
Other assets		57,332,000
Total assets acquired		1,739,273,000
Liabilities assumed:
Deposits		1,439,203,000
Other borrowings		63,439,000
Other liabilities		20,153,000
Total liabilities assumed		1,522,795,000
Net assets acquired		216,478,000
Consideration paid
Cash		91,400,000
Common stock		166,515,000
Total consideration paid		257,915,000
Goodwill		$ 41,437,000
Banc Ed | Pro Forma
Consideration paid
Total revenues (net interest income plus non-interest income)			100,652,000,000
Net income			$ 27,390,000,000
Diluted earnings per common share (in dollars per share) | $ / shares			$ 0.49
IST | Non-interest expense
Merger agreement
Business acquisition expenses			$ 100,000	$ 200,000