Fair Value Measurements (Narrative) (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments recorded at fair value	$ 2,590,292,000	$ 685,797,000
Interest rate swap maturity period	30 years
Book value of other real estate owned (OREO) and repossessed assets	3,800,000
Private Equity Funds, Domestic [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments recorded at fair value	1,400,000
Cost basis of investments	11,200,000
Investments In Private Equity Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Maturity period of investments	10 years
Unfunded commitment for investments	5,000,000
Rabbi Trust [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost basis of investments	$ 5,100,000