Pro Forma Results of Combined Company Operations (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Business Acquisition, Pro Forma Information [Line Items]
Total Revenues	$ 717,505	$ 722,210
Net Income	$ 72,810	$ 46,221
Income per share
Basic	$ 1.88	$ 1.18
Diluted	$ 1.82	$ 1.15