Long-Term Debt - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended				9 Months Ended				1 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 sqft	Sep. 30, 2011	Dec. 31, 2011	Sep. 09, 2011	Sep. 30, 2012 Minimum [Member]	Sep. 30, 2012 Maximum [Member]	Sep. 30, 2012 Convertible Senior Notes [Member]	Sep. 30, 2012 Term Loan [Member]	May 31, 2012 Interest Rate Swap [Member]	Sep. 30, 2012 Interest Rate Swap [Member]	Sep. 30, 2012 Interest Rate Swap [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity under the revolving credit facility						$ 170,000,000
Increase in line of credit facility current borrowing capacity	195,000,000		195,000,000
Line of credit principal outstanding	40,000,000		40,000,000
Aggregate principal amount of letter of credit			10,300,000
Line of credit facility description variable rate basis			The base rate is, for any day, a rate of interest per annum equal to the highest of (i) the prime rate of interest announced from time to time by U.S. Bank or its parent, (ii) the sum of the federal funds rate for such day plus 0.50% per annum and (iii) the Eurodollar rate (without giving effect to the applicable margin) for a one month interest period on such day (or if such day is not a business day, the immediately preceding business day) plus 1.00%.
Line of credit facility basis spread on federal fund rate	0.50%		0.50%
Line of credit facility basis spread on euro dollar rate	1.00%		1.00%
Line of credit facility commitment fee percentage							0.25%	0.50%
Line of credit facility applicable margin on base rate loan							0.75%	1.75%
Line of credit facility applicable margin on Euro dollar loan							1.75%	2.75%
Ratio of debt to EBITDA			0.0275
Minimum fixed charge coverage ratio			1.75
Line of credit facility debt default minimum amount	20,000,000		20,000,000
Principal amount	187,000,000		187,000,000		187,000,000				187,000,000	48,600,000
Percentage of contractual interest rate	3.75%		3.75%							4.25%
Senior notes conversion ratio			31.9601
Debt instrument conversion price	$ 31.29		$ 31.29
Senior note effective interest rate	7.50%		7.50%
Maturity period based on US government securities									7 years
Senior notes debt maturity date			Oct. 01, 2014
Senior notes amortization period			24 months
Amount of equity component of notes net of deferred taxes	24,000,000		24,000,000
Purchase price for acquisition of property			81,000,000
Area covered by property			460,000
Euro Dollar interest rate terms			The Eurodollar rate is a per annum rate of interest equal to the greater of (a) the rate that is published in the Wall Street Journal as the London interbank offered rate for deposits in United States dollars, for a period of one month, two business days prior to the commencement of an Interest Period, multiplied by a statutory reserve rate established by the Board of Governors of the Federal Reserve System, or (b) 4.25%.
Term Loan Agreement													Nov. 30, 2018
Debt instrument increase in interest rate in case of default										5.00%
Notional amount of interest rate swap agreement											42,500,000
Swap Agreement											Mar. 01, 2013
LIBOR rate, description													One-month LIBOR plus 3.25%
LIBOR rate												3.25%	3.25%
Fixed rate												5.34%	5.34%
Fair value of the Swap Agreement	1,270,000		1,270,000									1,300,000	1,300,000
General and administrative expense recorded	$ 127,500,000	$ 99,610,000	$ 379,208,000	$ 290,967,000								$ 200,000	$ 1,300,000