Shareholders' Equity and Minimum Regulatory Capital Requirements - Additional Information (Detail) - USD ($)					3 Months Ended
	Oct. 20, 2015	Jan. 30, 2015	Jul. 15, 2014	Sep. 24, 2013	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Aug. 31, 2010
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Period of retained net profits					2 years
Approved dividend to Company by subsidiary		$ 199,400,000	$ 56,000,000	$ 105,000,000
Conservation buffer, actual					5.70%
Dividend declared per share	$ 0.10
Stock repurchase, authorized amount					$ 400,000,000.0
Common shares repurchased					4,390,000	$ 24,996,000
Stock repurchased					$ 298,639,000		$ 294,249,000
Stock repurchased (in shares)					12,345,000		12,196,000
Share Repurchase Plan
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common shares repurchased					$ 4,400,000
Common shares repurchased (in shares)					148,300
Average price of common shares repurchased (in dollars per share)					$ 29.61
Stock repurchased					$ 298,600,000
Stock repurchased (in shares)					12,344,660
Stock repurchased, average price per share (in dollars per share)					$ 24.19
Remaining availability for future share repurchases					$ 101,400,000
Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital to risk-weighted assets (at least)					13.70%		13.70%
Tier 1 capital to risk-weighted assets (at least)					13.00%		12.90%
Tier 1 capital ratio, minimum leverage ratio					11.10%		11.10%
Bank | Minimum
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital to risk-weighted assets (at least)								12.00%
Tier 1 capital to risk-weighted assets (at least)								11.00%
Tier 1 capital ratio, minimum leverage ratio								10.00%