Fair Value Measurements Changes in Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Level 3 Inputs (Details) - Fair Value, Measurements, Recurring [Member] - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pooled Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 707	$ 422
Unrealized adjustment to fair value	158	0
(Premium amortization) discount accretion	0	0
Balance, end of period	865	422
Single-issuer Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	3,050	2,450
Unrealized adjustment to fair value	42	297
(Premium amortization) discount accretion	3	3
Balance, end of period	3,095	2,750
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	98,668	97,256
Unrealized adjustment to fair value	4,381	86
(Premium amortization) discount accretion	0	97
Balance, end of period	$ 103,049	$ 97,439