Share-Based Payment Arrangements - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2014 Bank	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised	$ 0.2	$ 0.1
Unrecognized compensation cost	31.7
Weighted-average period in years	3 years 1 month 6 days
Total fair value of shares vested	$ 10	$ 1
Shareholder return period	3 years
Number of peer group of regional banks	50
Performance Share Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted to key members of executives and senior management	69,857
Weighted average fair value of shares granted	$ 38.14
Percentage of maximum number of shares earned of target award	200.00%