Loans, Loans by Past Due Status (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Summarized details of Loans
Current	$ 22,785,019	$ 20,555,250
Financing Receivable, Recorded Investment, Nonaccrual Status	127,901	208,546
Loans and Leases Receivable, Net of Deferred Income	22,940,429	20,784,991
Nonaccrual Loans, Current Portion	$ 74,000	$ 135,000
Percent of current nonaccrual loans	58.00%	65.00%
30-59 Days Past Due
Summarized details of Loans
Total Past Due	$ 21,550	$ 16,861
60-89 Days Past Due
Summarized details of Loans
Total Past Due	3,795	2,467
90 Days or More Past Due
Summarized details of Loans
Total Past Due	2,165	1,867
Commercial and industrial
Summarized details of Loans
Current	7,356,187	6,286,369
Financing Receivable, Recorded Investment, Nonaccrual Status	41,021	112,786
Loans and Leases Receivable, Net of Deferred Income	7,398,044	6,399,693
Commercial and industrial | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	187	170
Commercial and industrial | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	338	101
Commercial and industrial | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	311	267
Commercial real estate — owner occupied
Summarized details of Loans
Current	913,787	779,421
Financing Receivable, Recorded Investment, Nonaccrual Status	3,957	22,740
Loans and Leases Receivable, Net of Deferred Income	920,443	802,209
Commercial real estate — owner occupied | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	2,580	48
Commercial real estate — owner occupied | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	119	0
Commercial real estate — owner occupied | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	0	0
Commercial and business lending
Summarized details of Loans
Current	8,269,974	7,065,790
Financing Receivable, Recorded Investment, Nonaccrual Status	44,978	135,526
Loans and Leases Receivable, Net of Deferred Income	8,318,487	7,201,902
Commercial and business lending | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	2,767	218
Commercial and business lending | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	457	101
Commercial and business lending | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	311	267
Commercial real estate — investor
Summarized details of Loans
Current	3,745,835	3,310,000
Financing Receivable, Recorded Investment, Nonaccrual Status	1,952	4,729
Loans and Leases Receivable, Net of Deferred Income	3,751,554	3,315,254
Commercial real estate — investor | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	2,954	374
Commercial real estate — investor | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	813	0
Commercial real estate — investor | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	0	151
Real estate construction
Summarized details of Loans
Current	1,333,722	1,450,459
Financing Receivable, Recorded Investment, Nonaccrual Status	979	974
Loans and Leases Receivable, Net of Deferred Income	1,335,031	1,451,684
Real estate construction | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	330	168
Real estate construction | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	0	83
Real estate construction | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	0	0
Commercial real estate lending
Summarized details of Loans
Current	5,079,557	4,760,459
Financing Receivable, Recorded Investment, Nonaccrual Status	2,931	5,703
Loans and Leases Receivable, Net of Deferred Income	5,086,585	4,766,938
Commercial real estate lending | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	3,284	542
Commercial real estate lending | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	813	83
Commercial real estate lending | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	0	151
Total commercial
Summarized details of Loans
Current	13,349,531	11,826,249
Financing Receivable, Recorded Investment, Nonaccrual Status	47,909	141,229
Loans and Leases Receivable, Net of Deferred Income	13,405,072	11,968,840
Total commercial | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	6,051	760
Total commercial | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	1,270	184
Total commercial | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	311	418
Residential mortgage
Summarized details of Loans
Current	8,200,432	7,483,350
Financing Receivable, Recorded Investment, Nonaccrual Status	67,574	53,632
Loans and Leases Receivable, Net of Deferred Income	8,277,712	7,546,534
Residential mortgage | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	9,272	9,186
Residential mortgage | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	434	366
Residential mortgage | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	0	0
Home equity
Summarized details of Loans
Current	876,085	863,465
Financing Receivable, Recorded Investment, Nonaccrual Status	12,339	13,514
Loans and Leases Receivable, Net of Deferred Income	894,473	883,804
Home equity | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	4,826	5,688
Home equity | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	1,223	1,137
Home equity | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	0	0
Other consumer
Summarized details of Loans
Current	358,970	382,186
Financing Receivable, Recorded Investment, Nonaccrual Status	79	171
Loans and Leases Receivable, Net of Deferred Income	363,171	385,813
Other consumer | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	1,401	1,227
Other consumer | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	868	780
Other consumer | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	1,853	1,449
Total consumer
Summarized details of Loans
Current	9,435,487	8,729,001
Financing Receivable, Recorded Investment, Nonaccrual Status	79,992	67,317
Loans and Leases Receivable, Net of Deferred Income	9,535,357	8,816,151
Total consumer | 30-59 Days Past Due
Summarized details of Loans
Total Past Due	15,499	16,101
Total consumer | 60-89 Days Past Due
Summarized details of Loans
Total Past Due	2,525	2,283
Total consumer | 90 Days or More Past Due
Summarized details of Loans
Total Past Due	$ 1,853	$ 1,449