Investment Securities (Schedule of Investment Securities) (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale securities
Amortized Cost	$ 3,086,824,000	$ 2,185,494,000
Gross unrealized gains	30,467,000	6,780,000
Gross unrealized losses	(11,077,000)	(66,193,000)
Fair Value	3,106,214,000	2,126,081,000
Held-to-maturity securities
Amortized Cost	1,134,400,000	1,067,439,000
Gross unrealized gains	9,695,000	2,241,000
Gross unrealized losses	(5,699,000)	(33,584,000)
Fair Value	1,138,396,000	1,036,096,000
Equity securities with readily determinable fair value
Amortized Cost	48,044,000	34,410,000
Gross unrealized gains	3,511,000	1,532,000
Gross unrealized losses	(715,000)	(1,225,000)
Fair Value	50,840,000	34,717,000
U.S. Treasury
Available-for-sale securities
Amortized Cost	120,275,000	126,199,000
Gross unrealized gains	813,000	391,000
Gross unrealized losses	0	(186,000)
Fair Value	121,088,000	126,404,000
U.S. Government agencies
Available-for-sale securities
Amortized Cost	365,639,000	139,420,000
Gross unrealized gains	3,557,000	917,000
Gross unrealized losses	(3,754,000)	(30,000)
Fair Value	365,442,000	140,307,000
Held-to-maturity securities
Amortized Cost	902,974,000	814,864,000
Gross unrealized gains	2,159,000	1,141,000
Gross unrealized losses	(5,460,000)	(28,576,000)
Fair Value	899,673,000	787,429,000
Municipal
Available-for-sale securities
Amortized Cost	141,701,000	136,831,000
Gross unrealized gains	3,785,000	2,427,000
Gross unrealized losses	(168,000)	(768,000)
Fair Value	145,318,000	138,490,000
Held-to-maturity securities
Amortized Cost	231,426,000	252,575,000
Gross unrealized gains	7,536,000	1,100,000
Gross unrealized losses	(239,000)	(5,008,000)
Fair Value	238,723,000	248,667,000
Corporate notes, financial issuers
Available-for-sale securities
Amortized Cost	97,051,000	97,079,000
Gross unrealized gains	761,000	35,000
Gross unrealized losses	(4,002,000)	(7,069,000)
Fair Value	93,810,000	90,045,000
Corporate notes, other
Available-for-sale securities
Amortized Cost	1,000,000	1,000,000
Gross unrealized gains	31,000	0
Gross unrealized losses	0	0
Fair Value	1,031,000	1,000,000
Mortgage-backed securities
Available-for-sale securities
Amortized Cost	2,328,383,000	1,641,146,000
Gross unrealized gains	21,240,000	2,510,000
Gross unrealized losses	(3,013,000)	(57,317,000)
Fair Value	2,346,610,000	1,586,339,000
Collateralized mortgage obligations
Available-for-sale securities
Amortized Cost	32,775,000	43,819,000
Gross unrealized gains	280,000	500,000
Gross unrealized losses	(140,000)	(823,000)
Fair Value	32,915,000	$ 43,496,000
Subprime
Available-for-sale securities
Fair Value	$ 0