Securities - Amortized Cost, Estimated Fair Value and Credit Rating of Corporate Debt Securities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 874,119	$ 772,975
Estimated Fair Value	895,897	$ 777,290
Chase Capital
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	10,000
Estimated Fair Value	$ 8,804
Credit Rating Moody’s/ S&P	Baa1/BBB-
Wells Fargo Capital
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 5,000
Estimated Fair Value	$ 4,392
Credit Rating Moody’s/ S&P	A1/BBB
Huntington Capital
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 5,000
Estimated Fair Value	$ 4,268
Credit Rating Moody’s/ S&P	Baa2/BB+
Keycorp Capital
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 5,000
Estimated Fair Value	$ 4,305
Credit Rating Moody’s/ S&P	Baa2/BB+
PNC Capital
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 5,000
Estimated Fair Value	$ 4,303
Credit Rating Moody’s/ S&P	Baa1/BBB-
SunTrust Capital
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 5,000
Estimated Fair Value	$ 4,281
Credit Rating Moody’s/ S&P	Not Rated/BBB-
State Street Capital
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 3,332
Estimated Fair Value	$ 2,855
Credit Rating Moody’s/ S&P	A3/BBB
Corporate debt securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 38,332
Estimated Fair Value	$ 33,208