Summary of Significant Accounting Policies (Correction of Immaterial Errors) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended							9 Months Ended
	Dec. 31, 2016	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Increase (decrease) in interest income on taxable investment securities		$ 24,435				$ 13,979			$ 48,633	$ 43,130
Decrease (increase) in unrealized losses on taxable investment securities		(29,262)				4,118			(75,479)	22,581
Interest and fees on loans and leases		246,410				226,068			718,021	645,780
Total interest income		276,242				243,463			780,381	699,434
Net interest income		241,368				223,211			691,249	642,732
Net interest income after provision for loan and lease losses		229,657				211,214			652,563	608,406
Gain on loan sales, net		2,772				9,260			5,350	14,324
Non-interest income		72,388				76,693			222,606	208,037
Income before provision for income taxes		122,753				99,553			314,192	261,354
Provision for income taxes		31,772				35,746			78,240	94,292
Net income		90,981	$ 65,999	$ 78,972	$ 75,251	63,807	$ 57,219	$ 46,036	235,952	167,062
Dividends and undistributed earnings allocated to participating securities		5				14			15	40
Net earnings available to common shareholders		$ 90,976				$ 63,793			$ 235,937	$ 167,022
Basic (in usd per share)		$ 0.41				$ 0.29			$ 1.07	$ 0.76
Diluted (in usd per share)		$ 0.41				$ 0.29			$ 1.07	$ 0.76
Loans and leases		$ 19,854,033			19,019,192	$ 18,614,438			$ 19,854,033	$ 18,614,438
Loans and leases, net		19,710,007			18,878,584				19,710,007
Total assets		26,615,067			25,680,447				26,615,067
Deferred tax liability, net		22,413			21,930				22,413
Total liabilities		22,611,174			21,711,080				22,611,174
Retained earnings		568,619			477,101				568,619
Total shareholders' equity		4,003,893			3,969,367				4,003,893
Total liabilities and shareholders' equity		26,615,067			25,680,447				26,615,067
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		67,396				66,334			175,559	180,881
Net cash provided by operating activities									318,601	250,517
Net cash used in investing activities									847,206	1,543,611
Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Interest and fees on loans and leases						223,321				642,315
Total interest income						240,716				695,969
Net interest income						220,464				639,267
Net interest income after provision for loan and lease losses						208,467				604,941
Gain on loan sales, net						7,969				13,033
Non-interest income						75,402				206,746
Income before provision for income taxes						95,515				256,598
Provision for income taxes						34,182				92,450
Net income					81,871	61,333	56,812	46,003		164,148
Net earnings available to common shareholders						$ 61,319				$ 164,108
Basic (in usd per share)						$ 0.28				$ 0.75
Diluted (in usd per share)						$ 0.28				$ 0.74
Loans and leases					19,080,184
Loans and leases, net					18,939,576
Total assets					25,741,439
Deferred tax liability, net					37,503
Total liabilities					21,726,653
Retained earnings					522,520
Total shareholders' equity					4,014,786
Total liabilities and shareholders' equity					25,741,439
Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Interest and fees on loans and leases						$ 2,747				$ 3,465
Total interest income						2,747				3,465
Net interest income						2,747				3,465
Net interest income after provision for loan and lease losses						2,747				3,465
Gain on loan sales, net						1,291				1,291
Non-interest income						1,291				1,291
Income before provision for income taxes						4,038				4,756
Provision for income taxes						1,564				1,842
Net income					(6,620)	2,474	$ 407	$ 33		2,914
Net earnings available to common shareholders						$ 2,474				$ 2,914
Basic (in usd per share)						$ 0.01				$ 0.01
Diluted (in usd per share)						$ 0.01				$ 0.02
Loans and leases					(60,992)
Loans and leases, net					(60,992)
Total assets					(60,992)
Deferred tax liability, net					(15,573)
Total liabilities					(15,573)
Retained earnings					(45,419)
Total shareholders' equity					(45,419)
Total liabilities and shareholders' equity					$ (60,992)
Prior period adjustment, Note 1	$ (41,713)
Residential mortgage-backed securities and collateralized mortgage obligations
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Available for sale, at fair value			$ 2,500,000
Out of Period Correction
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Increase (decrease) in interest income on taxable investment securities		7,000							(169)
Decrease (increase) in unrealized losses on taxable investment securities		$ (7,000)							$ 169
Prior period adjustment, Note 1	$ (41,700)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest						$ 2,500				$ 2,900
Net cash provided by operating activities										3,500
Net cash used in investing activities										$ (3,500)