Investment Securities (Contractual Maturities of Investment Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available-for-sale securities
Available-for-sale securities, due in one year or less, amortized cost	$ 82,206	$ 300,833
Available-for-sale securities, due in one year or less, fair value	82,153	299,285
Available-for-sale securities, due in one to five years, amortized cost	168,855	97,019
Available-for-sale securities, due in one to five years, fair value	169,307	97,326
Available-for-sale securities, due in five to ten years, amortized cost	121,129	33,947
Available-for-sale securities, due in five to ten years, fair value	115,206	35,029
Available-for-sale securities, due after ten years, amortized cost	128,339	15,249
Available-for-sale securities, due after ten years, fair value	129,580	15,499
Available-for-sale securities, amortized cost	2,185,494	1,833,069
Available-for-sale securities, fair value	2,126,081	1,803,666
Available-for-sale securities, amortized cost		1,833,069
Available-for-sale securities, fair value		1,803,666
Held-to-maturity securities
Held-to-maturity securities, due in one year or less, amortized cost	10,009	170
Held-to-maturity securities, due in one year or less, fair value	9,979	171
Held-to-maturity securities, due in one to five years, amortized cost	29,436	38,392
Held-to-maturity securities, due in one to five years, fair value	28,995	38,012
Held-to-maturity securities, due in five to ten years, amortized cost	295,897	205,227
Held-to-maturity securities, due in five to ten years, fair value	290,206	203,680
Held-to-maturity securities, due after ten years, amortized cost	732,097	582,660
Held-to-maturity securities, due after ten years, fair value	706,916	570,653
Held-to-maturity securities	1,067,439	826,449
Held-to-maturity securities, fair value	1,036,096	812,516
Mortgage-backed
Available-for-sale securities
Available-for-sale securities, without single maturity, amortized cost	1,684,965	1,351,787
Available-for-sale securities, without single maturity, fair value	1,629,835	1,319,725
Equity securities with readily determinable fair value
Available-for-sale securities
Available-for-sale equity securities, amortized cost		34,234
Available-for-sale equity securities, fair value		36,802
Available-for-sale securities, amortized cost	0	34,234
Available-for-sale securities, fair value	$ 0	$ 36,802