Earnings Per Share - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share Disclosure [Line Items]
Convertible Notes	$ 172,500	$ 172,500	$ 172,500
Number of common shares issue upon conversion		4,248,761
Average price of common stock	$ 41.38	$ 41.38
Convertible notes conversion price	$ 40.60	$ 40.60
Shares relating to the conversion premium	20,022	20,022