Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Goodwill And Other Intangible Assets [Line Items]
Beginning Balance	$ 180,867
Discontinued assets ─ goodwill and other intangibles, net	0	$ (47,529)
Ending Balance	180,867	180,867
Segment, Continuing and Discontinued Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Beginning Balance	180,867	228,396
Ending Balance		180,867
Continuing Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Beginning Balance	180,867
Ending Balance	180,867	180,867
Commercial Banking [Member]
Goodwill And Other Intangible Assets [Line Items]
Discontinued assets ─ goodwill and other intangibles, net	0	0
Commercial Banking [Member] | Segment, Continuing and Discontinued Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Beginning Balance	59,419	59,419
Ending Balance		59,419
Commercial Banking [Member] | Continuing Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Beginning Balance	59,419
Ending Balance	59,419	59,419
Institutional Banking [Member]
Goodwill And Other Intangible Assets [Line Items]
Discontinued assets ─ goodwill and other intangibles, net	0	(47,529)
Institutional Banking [Member] | Segment, Continuing and Discontinued Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Beginning Balance	51,332	98,861
Ending Balance		51,332
Institutional Banking [Member] | Continuing Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Beginning Balance	51,332
Ending Balance	51,332	51,332
Personal Banking [Member]
Goodwill And Other Intangible Assets [Line Items]
Discontinued assets ─ goodwill and other intangibles, net	0	0
Personal Banking [Member] | Segment, Continuing and Discontinued Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Beginning Balance	70,116	70,116
Ending Balance		70,116
Personal Banking [Member] | Continuing Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Beginning Balance	70,116
Ending Balance	70,116	70,116
Healthcare Services [Member]
Goodwill And Other Intangible Assets [Line Items]
Discontinued assets ─ goodwill and other intangibles, net	0	0
Healthcare Services [Member] | Segment, Continuing and Discontinued Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Beginning Balance	0	0
Ending Balance		0
Healthcare Services [Member] | Continuing Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Beginning Balance	0
Ending Balance	$ 0	$ 0