Earnings per Share - Schedule Of Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Earnings Per Share [Abstract]
Net income attributable to continuing operations	$ 33,119		$ 18,674		$ 22,132		$ 13,522		$ 24,929		$ 18,987		$ 23,315		$ 18,627		$ 87,447		$ 85,858		$ 87,557
Preferred stock dividends																	(41)		(41)		(41)
Income from continuing operations available to common equity																	87,406		85,817		87,516
Dividends and undistributed earnings allocated to participating securities																	(546)		(643)		(836)
Income from continuing operations available to common shareholders																	86,860		85,174		86,680
Net income attributable to discontinued operations	(432)		631		356		504		482		514		734		659		1,059		2,389		3,080
Preferred stock dividends																	(1)		(1)		(1)
Income from discontinued operations available to common equity																	1,058		2,388		3,079
Dividends and undistributed earnings allocated to participating securities																	(7)		(18)		(29)
Income from discontinued operations available to common shareholders																	$ 1,051		$ 2,370		$ 3,050
Basic weighted-average shares outstanding																	37,138		36,868		36,564
Stock options and other stock compensation																	590		582		478
Diluted weighted-average shares outstanding																	37,728		37,450		37,042
Antidilutive stock options																	0		15		744
Earnings per share attributable to continuing operations:
Income from continuing operations, Basic (dollars per share)	$ 0.88	[1]	$ 0.50	[1]	$ 0.59	[1]	$ 0.37	[1]	$ 0.67	[1]	$ 0.51	[1]	$ 0.63	[1]	$ 0.50	[1]	$ 2.34	[1]	$ 2.31	[1]	$ 2.37
Income from continuing operations, Diluted (dollars per share)	$ 0.87	[1]	$ 0.49	[1]	$ 0.58	[1]	$ 0.36	[1]	$ 0.66	[1]	$ 0.51	[1]	$ 0.62	[1]	$ 0.49	[1]	$ 2.30	[1]	$ 2.28	[1]	$ 2.34
Earnings per share attributable to discontinued operations:
Income from discontinued operations, Basic (dollars per share)	$ (0.01)	[1]	$ 0.02	[1]	$ 0.01	[1]	$ 0.01	[1]	$ 0.01	[1]	$ 0.01	[1]	$ 0.02	[1]	$ 0.02	[1]	$ 0.03	[1]	$ 0.06	[1]	$ 0.08
Income from discontinued operations, Diluted (dollars per share)	$ (0.01)	[1]	$ 0.02	[1]	$ 0.01	[1]	$ 0.01	[1]	$ 0.01	[1]	$ 0.01	[1]	$ 0.02	[1]	$ 0.02	[1]	$ 0.03	[1]	$ 0.06	[1]	$ 0.08

[1] Per share amounts are calculated independently for each period presented; therefore, the sum of the quarterly per share amounts may not equal the per share amounts for the year.