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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pooled Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 865	$ 422	$ 707	$ 422
Unrealized adjustment to fair value	10	0	168	0
(Premium amortization) discount accretion	0	0	0	0
Balance, end of period	875	422	875	422
Single-issuer Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	3,095	2,750	3,050	2,450
Unrealized adjustment to fair value	102	22	144	319
(Premium amortization) discount accretion	3	3	6	6
Balance, end of period	3,200	2,775	3,200	2,775
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	103,049	97,439	98,668	97,256
Unrealized adjustment to fair value	73	386	4,454	472
(Premium amortization) discount accretion	0	98	0	195
Balance, end of period	$ 103,122	$ 97,923	$ 103,122	$ 97,923