Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands		Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		$ 7,300,421	$ 5,999,327
Derivative assets		4,691	2,869
Derivative liabilities		32,997	44,841
Total recurring fair value measurements - liabilities		4,900	5,600
Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		7,300,421	5,999,327
Mortgage loans held for sale		65,970
Derivative assets	[1]	109,453	150,180
Total fair value measurements		7,475,844	6,149,507
Derivative liabilities	[1]	44,318	55,257
Total recurring fair value measurements - liabilities		44,318	55,257
Recurring [Member] | U.S. Treasury And Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		404,146	213,370
Recurring [Member] | Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		319,295	326,725
Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		14,780	11,764
Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		3,471,550	2,629,811
Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		2,938,596	2,455,534
Recurring [Member] | Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		152,054	362,123
Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		7,300,421	5,999,327
Mortgage loans held for sale		65,970
Derivative assets	[1]	109,453	150,180
Total fair value measurements		7,475,844	6,149,507
Derivative liabilities	[1]	39,451	49,612
Total recurring fair value measurements - liabilities		39,451	49,612
Recurring [Member] | Level 2 [Member] | U.S. Treasury And Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		404,146	213,370
Recurring [Member] | Level 2 [Member] | Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		319,295	326,725
Recurring [Member] | Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		14,780	11,764
Recurring [Member] | Level 2 [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		3,471,550	2,629,811
Recurring [Member] | Level 2 [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		2,938,596	2,455,534
Recurring [Member] | Level 2 [Member] | Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities		152,054	362,123
Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	[1]	4,867	5,645
Total recurring fair value measurements - liabilities		$ 4,867	$ 5,645

[1] For further disaggregation of derivative assets and liabilities, see Note 5 - Derivatives.