Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest income
Interest and fees on loans		$ 976,990	$ 749,000	$ 659,538
Interest and dividends on investment securities
Taxable		119,741	96,909	95,152
Tax-exempt		44,782	32,977	32,049
Other interest		12,623	7,719	4,829
Total interest income		1,154,137	886,605	791,568
Interest expense
Interest on deposits		176,118	94,025	50,335
Interest on Federal funds purchased and securities sold under agreements to repurchase		2,006	2,527	1,314
Interest on other short-term funding		186	293	248
Interest on FHLB advances		73,668	30,364	10,741
Interest on long-term funding		22,579	18,176	21,657
Total interest expense		274,557	145,385	84,295
Net interest income		879,580	741,220	707,273
Provision for credit losses		0	26,000	70,000
Net interest income after provision for credit losses		879,580	715,220	637,273
Noninterest income
Noninterest Income In Scope of Topic 606		290,084	262,175	252,651
Capital markets, net		20,120	19,642	22,059
Mortgage banking, net		19,911	19,360	38,121
Bank and corporate owned life insurance		13,951	16,250	14,371
Asset gains (losses), net (a)		(1,103)	(1,244)	(86)
Investment securities gains (losses), net		(1,985)	434	9,316
Other		9,051	9,523	8,519
Total noninterest income		355,568	332,680	352,883
Noninterest expense
Personnel		482,676	428,976	424,676
Technology		72,674	63,004	57,300
Occupancy		59,121	53,842	56,069
Business development and advertising		30,923	28,946	26,351
Equipment		23,243	21,201	21,489
Legal and professional		23,061	22,509	19,869
Card issuance and loan costs		12,386	11,760	13,641
Foreclosure / OREO expense, net		3,603	4,878	4,844
FDIC assessment		30,000	31,300	34,750
Other intangible amortization		8,159	1,959	2,093
Other		46,951	40,758	41,478
Total noninterest expense		821,799	709,133	702,560
Income before income taxes		413,349	338,767	287,596
Income tax expense		79,786	109,503	87,322
Net income		333,562	229,264	200,274
Preferred stock dividends		10,784	9,347	8,903
Net income available to common equity		$ 322,779	$ 219,917	$ 191,371
Earnings per common share
Basic		$ 1.92	$ 1.45	$ 1.27
Diluted		$ 1.89	$ 1.42	$ 1.26
Average common shares outstanding
Basic		167,345	150,877	148,769
Diluted		169,732	153,647	149,961
Tax planning in response to TCJA		(3.60%)	0.00%	0.00%
Insurance Commissions and Fees [Member]
Noninterest income
Noninterest Income In Scope of Topic 606		$ 89,511	$ 81,474	$ 80,795
Service charges and deposit account fees
Noninterest income
Noninterest Income In Scope of Topic 606		66,075	64,427	66,609
Card-Based and Loan Fees [Member]
Noninterest income
Service charges on deposit account fees		57,474	52,688	50,077
Trust and asset management fees
Noninterest income
Noninterest Income In Scope of Topic 606		54,316	50,191	46,867
Brokerage and advisory fees
Noninterest income
Noninterest Income In Scope of Topic 606		28,246	19,935	16,235
Operating Segments [Member] | Risk Management and Shared Serivies [Member]
Noninterest income
Asset gains (losses), net (a)	[1]	2,000
Noninterest expense
Acquisition related costs (b)		$ 29,002	$ 0	$ 0

[1] The year ended December 31, 2018 includes approximately $2 million of Bank Mutual acquisition related asset losses net of asset gains.