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, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 2,126,081	$ 1,803,666
Trading account securities	1,692	995
Equity securities with readily determinable fair value	34,717	0
Mortgage loans held-for-sale	264,070	313,592
Mortgage servicing rights	75,183	33,676	$ 19,103	$ 9,092
U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	126,404	143,822
U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	140,307	156,915
Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	138,490	115,352
Equity securities with readily determinable fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	36,802
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	1,692	995
Mortgage loans held-for-sale	264,070	313,592
Loans held-for-investment	93,857	33,717
Mortgage servicing rights	75,183	33,676
Nonqualified deferred compensations assets	11,282	11,065
Derivative assets	73,172	52,069
Total financial assets	2,680,054	2,248,780
Derivative Liabilities	68,088	35,671
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	126,404	143,822
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	1,692	995
Mortgage loans held-for-sale	264,070	313,592
Loans held-for-investment	82,510	0
Mortgage servicing rights	0	0
Nonqualified deferred compensations assets	11,282	11,065
Derivative assets	70,715	49,912
Total financial assets	2,352,587	1,954,448
Derivative Liabilities	68,088	35,671
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	0	0
Mortgage loans held-for-sale	0	0
Loans held-for-investment	11,347	33,717
Mortgage servicing rights	75,183	33,676
Nonqualified deferred compensations assets	0	0
Derivative assets	2,457	2,157
Total financial assets	201,063	150,510
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	126,404	143,822
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	126,404	143,822
Fair Value, Measurements, Recurring | U.S. Treasury | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring | U.S. Treasury | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
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	140,307	156,915
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	137,157	153,136
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	3,150	3,779
Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	138,490	115,352
Fair Value, Measurements, Recurring | Municipal | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,564	38,171
Fair Value, Measurements, Recurring | Municipal | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	108,926	77,181
Fair Value, Measurements, Recurring | Corporate notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	91,045	31,050
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	91,045	31,050
Fair Value, Measurements, Recurring | Corporate notes | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring | Mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,629,835	1,319,725
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	1,629,835	1,319,725
Fair Value, Measurements, Recurring | Mortgage-backed | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring | Equity securities with readily determinable fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		36,802
Equity securities with readily determinable fair value	34,717
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]
Available-for-sale securities		36,802
Equity securities with readily determinable fair value	34,717
Fair Value, Measurements, Recurring | Equity securities with readily determinable fair value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		$ 0
Equity securities with readily determinable fair value	$ 0