Fair Value of Assets and Liabilities (Summary of Balances of Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 3,106,214	$ 2,126,081
Trading account securities	1,068	1,692
Equity securities with readily determinable fair value	50,840	34,717
Mortgage loans held-for-sale	377,313	264,070
MSRs	85,638	75,183	$ 33,676	$ 19,103
U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	121,088	126,404
U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	365,442	140,307
Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	145,318	138,490
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	1,068	1,692
Mortgage loans held-for-sale	377,313	264,070
Loans held-for-investment	132,718	93,857
MSRs	85,638	75,183
Nonqualified deferred compensations assets	14,213	11,282
Derivative assets	103,644	73,172
Total financial assets	3,871,648	2,680,054
Derivative liabilities	129,204	68,088
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	163,862	126,404
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	1,068	1,692
Mortgage loans held-for-sale	377,313	264,070
Loans held-for-investment	123,098	82,510
Nonqualified deferred compensations assets	14,213	11,282
Derivative assets	101,013	70,715
Total financial assets	3,495,301	2,352,587
Derivative liabilities	129,204	68,088
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-investment	9,620	11,347
MSRs	85,638	75,183
Derivative assets	2,631	2,457
Total financial assets	212,485	201,063
Fair Value, Measurements, Recurring | U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	121,088	126,404
Fair Value, Measurements, Recurring | U.S. Treasury | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	121,088	126,404
Fair Value, Measurements, Recurring | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	365,442	140,307
Fair Value, Measurements, Recurring | U.S. Government agencies | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	362,796	137,157
Fair Value, Measurements, Recurring | U.S. Government agencies | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,646	3,150
Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	145,318	138,490
Fair Value, Measurements, Recurring | Municipal | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	33,368	29,564
Fair Value, Measurements, Recurring | Municipal | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	111,950	108,926
Fair Value, Measurements, Recurring | Corporate notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	94,841	91,045
Fair Value, Measurements, Recurring | Corporate notes | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	94,841	91,045
Fair Value, Measurements, Recurring | Mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,379,525	1,629,835
Fair Value, Measurements, Recurring | Mortgage-backed | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	2,379,525	1,629,835
Fair Value, Measurements, Recurring | Equity securities with readily determinable fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities with readily determinable fair value	50,840	34,717
Fair Value, Measurements, Recurring | Equity securities with readily determinable fair value | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities with readily determinable fair value	42,774
Fair Value, Measurements, Recurring | Equity securities with readily determinable fair value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities with readily determinable fair value	$ 8,066	$ 34,717