| Pay vs Performance Disclosure | 12 Months Ended |
| Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) |
| Pay vs Performance Disclosure [Table] | | | |
| Pay vs Performance [Table Text Block] | Average Average Value of Initial Fixed $100 Summary Summary Compensation Investment Based On: Compensation Comp. Table Actually Company Peer Group Table Compensation Total Comp. Paid to Total Total Adjusted Total Comp. Actually Paid for Non-CEO Non-CEO Shareholder Shareholder Net One-Year Year for CEO (1) to CEO (3) NEOs (2) NEOs (3) Return Return (4) Income ROATCE (5) 2022 $ 11,657,989 $ 12,884,815 $ 4,162,215 $ 4,422,936 $ 108.69 $ 116.10 $ 414,169,000 21.1% 2021 $ 3,971,101 $ 4,414,151 $ 1,352,603 $ 1,504,898 $ 106.04 $ 124.74 $ 277,538,000 15.4% 2020 $ 3,708,472 $ 3,847,438 $ 1,250,625 $ 1,328,046 $ 93.93 $ 91.29 $ 226,409,000 14.6% (1) The CEO for each year is Jim Ryan, who began serving as our CEO in 2019. (2) Non-CEO NEOs for 2022 include Mike Scudder, Jim Sandgren, Mark Sander and Brendon Falconer. (3) To calculate compensation actually paid for the CEO and the average non-CEO NEOs, the following adjustments were made to the Summary Compensation Table total compensation, calculated in accordance with the SEC methodology for determining compensation actually paid for each year shown, excluding rows that are not applicable for the years presented: 2022 2021 2020 Other NEOs Other NEOs Other NEOs CEO Average CEO Average CEO Average Summary Compensation Table (SCT) Total $ 11,657,989 $ 4,162,215 $ 3,971,101 $ 1,352,603 $ 3,708,472 $ 1,250,625 Deduct: grant date fair value of equity awards granted during fiscal year (FY) $ 7,736,725 2,030,809 $ 1,540,832 $ 371,607 $ 1,424,200 $ 378,303 Add: fair value (FV) as of FY-end of equity awards granted during the year that are outstanding and unvested as of FY-end $ 8,122,095 $ 2,162,267 $ 1,587,472 $ 382,862 $ 1,198,673 $ 318,399 Add: change as of end of FY in FV of awards granted in any prior year that are outstanding and unvested as of FY-end $ 692,721 $ 102,279 $ 242,043 $ 62,209 $ 261,685 $ 80,212 Add: change as of the vesting date (from end of prior FY) in FV for any equity awards granted in any prior year that vested during or at the end of the FY $ 34,096 $ (6,661) $ 112,394 $ 57,214 $ 64,863 $ 36,006 Add: value of dividends or other earnings paid on stock or option awards not otherwise included in SCT $ 114,639 $ 33,645 $ 41,973 $ 21,616 $ 37,946 $ 21,107 Compensation Actually Paid $ 12,884,815 $ 4,422,936 $ 4,414,151 $ 1,504,898 $ 3,847,438 $ 1,328,046 (4) The Company has chosen to use the KRX Index for its peer group. (5) This non-GAAP financial measure excludes certain items, such as current expected credit loss (“CECL”) Day 1 non-PCD provision expense, merger related charges associated with completed acquisitions, gain on sale of health savings accounts, property optimization charges and net securities gains/losses. The equivalent GAAP measure for one-year ROATCE was 16.3% , 14.89% and 13.27% for 2022, 2021 and 2020, respectively. Reference is made to the non-GAAP reconciliation included in the Company’s annual report on Form 10-K for the year ended December 31, 2022 . Reference is made to the non-GAAP reconciliation included in the Company’s annual report on Form 10-K for the year ended December 31, 2022. | | |
| Company Selected Measure Name | Adjusted One-Year ROATCE | | |
| Named Executive Officers, Footnote [Text Block] | (1) The CEO for each year is Jim Ryan, who began serving as our CEO in 2019. (2) Non-CEO NEOs for 2022 include Mike Scudder, Jim Sandgren, Mark Sander and Brendon Falconer. | | |
| Peer Group Issuers, Footnote [Text Block] | 2022 2021 2020 Other NEOs Other NEOs Other NEOs CEO Average CEO Average CEO Average Summary Compensation Table (SCT) Total $ 11,657,989 $ 4,162,215 $ 3,971,101 $ 1,352,603 $ 3,708,472 $ 1,250,625 Deduct: grant date fair value of equity awards granted during fiscal year (FY) $ 7,736,725 2,030,809 $ 1,540,832 $ 371,607 $ 1,424,200 $ 378,303 Add: fair value (FV) as of FY-end of equity awards granted during the year that are outstanding and unvested as of FY-end $ 8,122,095 $ 2,162,267 $ 1,587,472 $ 382,862 $ 1,198,673 $ 318,399 Add: change as of end of FY in FV of awards granted in any prior year that are outstanding and unvested as of FY-end $ 692,721 $ 102,279 $ 242,043 $ 62,209 $ 261,685 $ 80,212 Add: change as of the vesting date (from end of prior FY) in FV for any equity awards granted in any prior year that vested during or at the end of the FY $ 34,096 $ (6,661) $ 112,394 $ 57,214 $ 64,863 $ 36,006 Add: value of dividends or other earnings paid on stock or option awards not otherwise included in SCT $ 114,639 $ 33,645 $ 41,973 $ 21,616 $ 37,946 $ 21,107 Compensation Actually Paid $ 12,884,815 $ 4,422,936 $ 4,414,151 $ 1,504,898 $ 3,847,438 $ 1,328,046 | | |
| PEO Total Compensation Amount | $ 11,657,989 | $ 3,971,101 | $ 3,708,472 |
| PEO Actually Paid Compensation Amount | $ 12,884,815 | 4,414,151 | 3,847,438 |
| Adjustment To PEO Compensation, Footnote [Text Block] | (3) To calculate compensation actually paid for the CEO and the average non-CEO NEOs, the following adjustments were made to the Summary Compensation Table total compensation, calculated in accordance with the SEC methodology for determining compensation actually paid for each year shown, excluding rows that are not applicable for the years presented: 2022 2021 2020 Other NEOs Other NEOs Other NEOs CEO Average CEO Average CEO Average Summary Compensation Table (SCT) Total $ 11,657,989 $ 4,162,215 $ 3,971,101 $ 1,352,603 $ 3,708,472 $ 1,250,625 Deduct: grant date fair value of equity awards granted during fiscal year (FY) $ 7,736,725 2,030,809 $ 1,540,832 $ 371,607 $ 1,424,200 $ 378,303 Add: fair value (FV) as of FY-end of equity awards granted during the year that are outstanding and unvested as of FY-end $ 8,122,095 $ 2,162,267 $ 1,587,472 $ 382,862 $ 1,198,673 $ 318,399 Add: change as of end of FY in FV of awards granted in any prior year that are outstanding and unvested as of FY-end $ 692,721 $ 102,279 $ 242,043 $ 62,209 $ 261,685 $ 80,212 Add: change as of the vesting date (from end of prior FY) in FV for any equity awards granted in any prior year that vested during or at the end of the FY $ 34,096 $ (6,661) $ 112,394 $ 57,214 $ 64,863 $ 36,006 Add: value of dividends or other earnings paid on stock or option awards not otherwise included in SCT $ 114,639 $ 33,645 $ 41,973 $ 21,616 $ 37,946 $ 21,107 Compensation Actually Paid $ 12,884,815 $ 4,422,936 $ 4,414,151 $ 1,504,898 $ 3,847,438 $ 1,328,046 | | |
| Non-PEO NEO Average Total Compensation Amount | $ 4,162,215 | 1,352,603 | 1,250,625 |
| Non-PEO NEO Average Compensation Actually Paid Amount | $ 4,422,936 | 1,504,898 | 1,328,046 |
| Adjustment to Non-PEO NEO Compensation Footnote [Text Block] | (3) To calculate compensation actually paid for the CEO and the average non-CEO NEOs, the following adjustments were made to the Summary Compensation Table total compensation, calculated in accordance with the SEC methodology for determining compensation actually paid for each year shown, excluding rows that are not applicable for the years presented: 2022 2021 2020 Other NEOs Other NEOs Other NEOs CEO Average CEO Average CEO Average Summary Compensation Table (SCT) Total $ 11,657,989 $ 4,162,215 $ 3,971,101 $ 1,352,603 $ 3,708,472 $ 1,250,625 Deduct: grant date fair value of equity awards granted during fiscal year (FY) $ 7,736,725 2,030,809 $ 1,540,832 $ 371,607 $ 1,424,200 $ 378,303 Add: fair value (FV) as of FY-end of equity awards granted during the year that are outstanding and unvested as of FY-end $ 8,122,095 $ 2,162,267 $ 1,587,472 $ 382,862 $ 1,198,673 $ 318,399 Add: change as of end of FY in FV of awards granted in any prior year that are outstanding and unvested as of FY-end $ 692,721 $ 102,279 $ 242,043 $ 62,209 $ 261,685 $ 80,212 Add: change as of the vesting date (from end of prior FY) in FV for any equity awards granted in any prior year that vested during or at the end of the FY $ 34,096 $ (6,661) $ 112,394 $ 57,214 $ 64,863 $ 36,006 Add: value of dividends or other earnings paid on stock or option awards not otherwise included in SCT $ 114,639 $ 33,645 $ 41,973 $ 21,616 $ 37,946 $ 21,107 Compensation Actually Paid $ 12,884,815 $ 4,422,936 $ 4,414,151 $ 1,504,898 $ 3,847,438 $ 1,328,046 | | |
| Compensation Actually Paid vs. Total Shareholder Return [Text Block] | Total Shareholder Return. On an individual year basis, the Company’s TSR outperformed both the KRX Index and the Company’s peer group in 2020 and 2022. In 2021, the Company’s TSR was impacted by the announcement of the Merger with First Midwest, which is typical for a period of time following the announcement of a significant merger even when transactional financial metrics, such as ours, are favorable until such time as the combined financial performance is reported. Given this context, the Company’s TSR underperformed our peer group and the KRX Index in 2021. As a result, although we outperformed our benchmarks in two of the three individual years and delivered a positive cumulative three-year TSR, we modestly underperformed our peer group and the KRX Index on a cumulative basis for the three-year period ending December 31, 2022. | | |
| Compensation Actually Paid vs. Net Income [Text Block] | Net Income. The Company achieved record net income in 2021 and 2022. For 2022, results were positively impacted by the completion of our Merger with First Midwest, as well as robust broad-based total loan growth, net interest margin expansion, stable low-cost deposits, disciplined expense management and strong credit quality metrics. For 2020, even in the midst of the COVID-19 pandemic, the Company delivered strong net income results, primarily due to its commercial loan production, capital markets revenue and mortgage production, in addition to disciplined expense management and strong credit quality metrics. The Company does not currently use net income as one of its measures for its compensation decisions; however, net income is a key component of EPS, which is a measure used by the Company. | | |
| Compensation Actually Paid vs. Company Selected Measure [Text Block] | Adjusted One-Year ROATCE. The Company used adjusted one-year ROATCE as its company-selected measure. The Company used adjusted one-year ROATCE as a metric in its short-term incentive compensation awards for 2020, 2021 and 2022. ROATCE is a key indicator of performance and correlates . In 2020, 2021 and 2022, the Company exceeded its ROATCE performance targets and our one-year ROATCE has been in the top quartile of our peer group. | | |
| Tabular List [Table Text Block] | Tabular List The table below provides an unranked list of the most important financial measures used by the Company to link compensation actually paid (as defined by SEC rules) to the Company’s performance in 2022. Each of these financial metrics were used in determining short- or long-term incentive awards, as well as performance-based integration awards in 2022. Adjusted One-Year EPS Adjusted One-Year ROATCE Merger-Related Cost Savings Three-Year Relative TSR Three-Year Relative ROATCE | | |
| Total Shareholder Return Amount | $ 108.69 | 106.04 | 93.93 |
| Peer Group Total Shareholder Return Amount | 116.10 | 124.74 | 91.29 |
| Net Income (Loss) | $ 414,169,000 | $ 277,538,000 | $ 226,409,000 |
| Company Selected Measure Amount | 21.1 | 15.4 | 14.6 |
| PEO Name | Jim Ryan | | |
| Percentage of Equivalent GAAP Measure | 16.30% | 14.89% | 13.27% |
| Measure [Axis]: 1 | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Measure Name | Adjusted One-Year EPS | | |
| Measure [Axis]: 2 | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Measure Name | Adjusted One-Year ROATCE | | |
| Non-GAAP Measure Description [Text Block] | (5) This non-GAAP financial measure excludes certain items, such as current expected credit loss (“CECL”) Day 1 non-PCD provision expense, merger related charges associated with completed acquisitions, gain on sale of health savings accounts, property optimization charges and net securities gains/losses. The equivalent GAAP measure for one-year ROATCE was 16.3% , 14.89% and 13.27% for 2022, 2021 and 2020, respectively. Reference is made to the non-GAAP reconciliation included in the Company’s annual report on Form 10-K for the year ended December 31, 2022 . Reference is made to the non-GAAP reconciliation included in the Company’s annual report on Form 10-K for the year ended December 31, 2022. | | |
| Measure [Axis]: 3 | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Measure Name | Merger-Related Cost Savings | | |
| Measure [Axis]: 4 | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Measure Name | Three-Year Relative TSR | | |
| Measure [Axis]: 5 | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Measure Name | Three-Year Relative ROATCE | | |
| PEO [Member] | Deduct: grant date fair value of equity awards granted during fiscal year (FY) | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | $ 7,736,725 | $ 1,540,832 | $ 1,424,200 |
| PEO [Member] | Add: fair value (FV) as of FY-end of equity awards granted during the year that are outstanding and unvested as of FY-end | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 8,122,095 | 1,587,472 | 1,198,673 |
| PEO [Member] | Add: change as of end of FY in FV of awards granted in any prior year that are outstanding and unvested as of FY-end | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 692,721 | 242,043 | 261,685 |
| PEO [Member] | Add: change as of the vesting date (from end of prior FY) in FV for any equity awards granted in any prior year that vested during or at the end of the FY | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 34,096 | 112,394 | 64,863 |
| PEO [Member] | Add: value of dividends or other earnings paid on stock or option awards not otherwise included in SCT | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 114,639 | 41,973 | 37,946 |
| Non-PEO NEO [Member] | Deduct: grant date fair value of equity awards granted during fiscal year (FY) | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 2,030,809 | 371,607 | 378,303 |
| Non-PEO NEO [Member] | Add: fair value (FV) as of FY-end of equity awards granted during the year that are outstanding and unvested as of FY-end | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 2,162,267 | 382,862 | 318,399 |
| Non-PEO NEO [Member] | Add: change as of end of FY in FV of awards granted in any prior year that are outstanding and unvested as of FY-end | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 102,279 | 62,209 | 80,212 |
| Non-PEO NEO [Member] | Add: change as of the vesting date (from end of prior FY) in FV for any equity awards granted in any prior year that vested during or at the end of the FY | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (6,661) | 57,214 | 36,006 |
| Non-PEO NEO [Member] | Add: value of dividends or other earnings paid on stock or option awards not otherwise included in SCT | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | $ 33,645 | $ 21,616 | $ 21,107 |
