Business Segments - Schedule of Segment Reporting Information by Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Operating Statistics [Line Items]
Interest income, including loan fees	$ 58,813	$ 66,065
Total interest income	58,813	66,065
Interest expense	4,224	7,463
Total interest expense	4,224	7,463
Net interest income	54,589	58,602
Provision for credit losses
Net interest income after provision for credit losses	54,589	58,602
Noninterest income	6,745	5,256
Noninterest expense	30,798	30,212
Debt termination
Earnings before income taxes	30,536	33,646
Segment assets	6,265,767	6,506,083	6,363,364
Centers [Member]
Operating Statistics [Line Items]
Interest income, including loan fees	35,435	37,671
Credit for funds provided	6,312	6,347
Total interest income	41,747	44,018
Interest expense	1,499	2,051
Charge for funds used	1,073	1,097
Total interest expense	2,572	3,148
Net interest income	39,175	40,870
Provision for credit losses
Net interest income after provision for credit losses	39,175	40,870
Noninterest income	5,106	5,983
Noninterest expense	11,577	11,898
Debt termination
Earnings before income taxes	32,704	34,955
Segment assets	4,985,725	4,838,109
Treasury [Member]
Operating Statistics [Line Items]
Interest income, including loan fees	12,788	15,363
Total interest income	12,788	15,363
Interest expense	2,417	4,548
Charge for funds used	10,514	10,028
Total interest expense	12,931	14,576
Net interest income	(143)	787
Provision for credit losses
Net interest income after provision for credit losses	(143)	787
Noninterest income	2,094
Noninterest expense	184	195
Debt termination
Earnings before income taxes	1,767	592
Segment assets	2,622,402	2,749,505
Other [Member]
Operating Statistics [Line Items]
Interest income, including loan fees	10,590	13,031
Credit for funds provided	2,559	2,600
Total interest income	13,149	15,631
Interest expense	308	864
Charge for funds used	(2,716)	(2,178)
Total interest expense	(2,408)	(1,314)
Net interest income	15,557	16,945
Provision for credit losses
Net interest income after provision for credit losses	15,557	16,945
Noninterest income	(455)	(727)
Noninterest expense	19,037	18,119
Debt termination
Earnings before income taxes	(3,935)	(1,901)
Segment assets	788,016	922,575
Eliminations [Member]
Operating Statistics [Line Items]
Credit for funds provided	(8,871)	(8,947)
Total interest income	(8,871)	(8,947)
Charge for funds used	(8,871)	(8,947)
Total interest expense	(8,871)	(8,947)
Provision for credit losses
Debt termination
Segment assets	$ (2,130,376)	$ (2,004,106)