Investment Securities (Narrative) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($) security	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale [Line Items]
Equity securities without readily determinable fair values	$ 29,500								$ 29,500
Upward adjustments of equity securities without readily determinable fair values									505	$ 325	$ 0
Downward adjustments of equity securities without readily determinable fair values									106	0	0
Impairment of equity securities without readily determinable fair values									262	1,117	0
Income tax expense (benefit)	30,718	$ 35,480	$ 28,707	$ 29,499	$ 28,005	$ 30,866	$ 32,011	$ 26,085	124,404	116,967	132,315
Investment securities pledged as collateral	$ 1,700,000				$ 1,700,000				$ 1,700,000	1,700,000
Number of securities by a single non-government sponsored issuer exceeding 10% of shareholders' equity | security	0								0
Investment securities
Debt Securities, Available-for-sale [Line Items]
Income tax expense (benefit)									$ 913	$ (737)	$ 18