Segment Reporting - Financial Information for Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Financial information for the Company's operating segments
Net interest income (loss)	$ 130,318			$ 103,292			$ 343,462	$ 322,519
Provision for (recovery of provision for) credit losses	9,800			(1,200)			13,300	(1,200)
Noninterest income (loss)	41,186			50,755			115,858	179,402
Noninterest expense	101,574			103,999			293,873	328,711
Income (loss) before income taxes	60,130			51,248			152,147	174,410
Income tax expense (benefit)	13,563			11,185			32,355	35,572
Net income (loss)	46,567	$ 39,678	$ 33,547	40,063	$ 40,867	$ 57,908	119,792	138,838
Total assets	16,471,099			16,155,550			16,471,099	16,155,550	$ 16,810,311
Goodwill	946,291			939,683			946,291	939,683	939,683
Community Banks
Financial information for the Company's operating segments
Goodwill	943,524						943,524		936,916
Insurance
Financial information for the Company's operating segments
Goodwill	2,767						2,767		$ 2,767
Operating segments | Community Banks
Financial information for the Company's operating segments
Net interest income (loss)	134,528			106,506			356,040	332,234
Provision for (recovery of provision for) credit losses	9,800			(1,088)			13,300	(1,088)
Noninterest income (loss)	32,324			42,546			89,359	155,765
Noninterest expense	94,474			97,437			272,594	309,449
Income (loss) before income taxes	62,578			52,703			159,505	179,638
Income tax expense (benefit)	14,811			12,117			36,035	38,320
Net income (loss)	47,767			40,586			123,470	141,318
Total assets	16,369,592			16,040,728			16,369,592	16,040,728
Goodwill	943,524			936,916			943,524	936,916
Operating segments | Insurance
Financial information for the Company's operating segments
Net interest income (loss)	98			115			286	333
Provision for (recovery of provision for) credit losses	0			0			0	0
Noninterest income (loss)	3,123			2,835			8,831	8,558
Noninterest expense	2,190			2,095			6,311	6,005
Income (loss) before income taxes	1,031			855			2,806	2,886
Income tax expense (benefit)	268			220			734	740
Net income (loss)	763			635			2,072	2,146
Total assets	35,761			33,036			35,761	33,036
Goodwill	2,767			2,767			2,767	2,767
Operating segments | Wealth Management
Financial information for the Company's operating segments
Net interest income (loss)	794			404			1,813	1,184
Provision for (recovery of provision for) credit losses	0			(112)			0	(112)
Noninterest income (loss)	6,132			5,820			18,952	16,421
Noninterest expense	4,553			4,189			13,899	12,337
Income (loss) before income taxes	2,373			2,147			6,866	5,380
Income tax expense (benefit)	0			0			0	0
Net income (loss)	2,373			2,147			6,866	5,380
Total assets	73,704			67,204			73,704	67,204
Goodwill	0			0			0	0
Other
Financial information for the Company's operating segments
Net interest income (loss)	(5,102)			(3,733)			(14,677)	(11,232)
Provision for (recovery of provision for) credit losses	0			0			0	0
Noninterest income (loss)	(393)			(446)			(1,284)	(1,342)
Noninterest expense	357			278			1,069	920
Income (loss) before income taxes	(5,852)			(4,457)			(17,030)	(13,494)
Income tax expense (benefit)	(1,516)			(1,152)			(4,414)	(3,488)
Net income (loss)	(4,336)			(3,305)			(12,616)	(10,006)
Total assets	(7,958)			14,582			(7,958)	14,582
Goodwill	$ 0			$ 0			$ 0	$ 0