Shareholders' Equity Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 21,587	$ 56,673	$ (25,623)
Net change in unrealized gain (loss)		(41,521)	(46,803)	136,775
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		(112)	(503)	(1,216)
Interest expense, Subordinated debentures		0	121	296
Net impairment losses recognized in earnings		0	1,819	373
Gain on available for sale securities, net		(11,675)	(12,058)	(1,539)
Other comprehensive income (loss), before income taxes		(53,308)	(57,424)	134,689
Federal and state income taxes	[1]	(20,754)	(22,338)	52,393
Other comprehensive income (loss), net of income taxes		(32,554)	(35,086)	82,296
Ending balance		(10,967)	21,587	56,673
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		23,284	59,239	(23,175)
Net change in unrealized gain (loss)		(41,333)	(48,607)	136,050
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	0	0
Interest expense, Subordinated debentures		0	0	0
Net impairment losses recognized in earnings		0	1,819	373
Gain on available for sale securities, net		(11,675)	(12,058)	(1,539)
Other comprehensive income (loss), before income taxes		(53,008)	(58,846)	134,884
Federal and state income taxes	[1]	(20,637)	(22,891)	52,470
Other comprehensive income (loss), net of income taxes		(32,371)	(35,955)	82,414
Ending balance		(9,087)	23,284	59,239
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Perpetual Preferred, Equity Securities and Mutual Funds [Member]
Reclassification adjustments included in earnings: [Abstract]
Ending balance		2,400
Accumulated Unrealized Gain on AFS Securities Transferred to Investment Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		68	376	1,118
Net change in unrealized gain (loss)		0	0	0
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		(112)	(503)	(1,216)
Interest expense, Subordinated debentures		0	0	0
Net impairment losses recognized in earnings		0	0	0
Gain on available for sale securities, net		0	0	0
Other comprehensive income (loss), before income taxes		(112)	(503)	(1,216)
Federal and state income taxes	[1]	(44)	(195)	(474)
Other comprehensive income (loss), net of income taxes		(68)	(308)	(742)
Ending balance		0	68	376
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(1,765)	(2,868)	(3,311)
Net change in unrealized gain (loss)		(188)	1,804	725
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	0	0
Interest expense, Subordinated debentures		0	0	0
Net impairment losses recognized in earnings		0	0	0
Gain on available for sale securities, net		0	0	0
Other comprehensive income (loss), before income taxes		(188)	1,804	725
Federal and state income taxes	[1]	(73)	701	282
Other comprehensive income (loss), net of income taxes		(115)	1,103	443
Ending balance		(1,880)	(1,765)	(2,868)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		0	(74)	(255)
Net change in unrealized gain (loss)		0	0	0
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	0	0
Interest expense, Subordinated debentures		0	121	296
Net impairment losses recognized in earnings		0	0	0
Gain on available for sale securities, net		0	0	0
Other comprehensive income (loss), before income taxes		0	121	296
Federal and state income taxes	[1]	0	47	115
Other comprehensive income (loss), net of income taxes		0	74	181
Ending balance		$ 0	$ 0	$ (74)

[1] Calculated using 39% effective tax rate.