Long-Term Debt (Narrative) (Details) - USD ($) $ in Thousands		12 Months Ended
	Dec. 18, 2015	Dec. 31, 2017	Dec. 31, 2016	Mar. 09, 2015
Debt Instrument [Line Items]
Notes payable aggregate principal amount		$ 310,578
Other long-term debt maturity year		2053
Subordinated Notes [Member] | Subordinated Notes Payable, Maturing June 2045 [Member]
Debt Instrument [Line Items]
Notes payable issuance date		Mar. 09, 2015
Notes payable aggregate principal amount		$ 150,000	$ 150,000	$ 150,000
Notes payable maturity date		Jun. 15, 2045
Notes payable interest rate		5.95%
Notes payable beginning payment date		Jun. 01, 2015
Notes payable redemption date		Jun. 15, 2020
Subordinated Notes [Member] | Subordinated Notes Payable, Maturing April 2017 [Member]
Debt Instrument [Line Items]
Notes payable maturity date		Apr. 01, 2017
Notes payable interest rate		5.875%
Subordinated Notes [Member] | Subordinated Notes Payable Maturing On April 2017 [Member]
Debt Instrument [Line Items]
Notes payable aggregate principal amount			95,511
Term Note [Member] | Term Note Payable, Maturing December 2018 [Member]
Debt Instrument [Line Items]
Notes payable aggregate principal amount	$ 125,000	$ 89,200	107,100
Notes payable maturity date		Dec. 18, 2018
Notes payable reference for variable rate		LIBOR+1.50%
Percentage points added to reference rate	1.50%
Principal payment of term loan		$ 4,500
Other Long-Term Debt [Member]
Debt Instrument [Line Items]
Notes payable aggregate principal amount		$ 71,378	$ 89,196
Notes payable agreement period		7 years