Senior Note - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended				0 Months Ended	1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Senior Notes	Oct. 04, 2013 Senior Notes 5.75% Senior Notes	Oct. 04, 2013 Senior Notes 5.75% Senior Notes	Dec. 31, 2013 Senior Notes 5.75% Senior Notes	Dec. 31, 2013 Senior Notes 5.75% Senior Notes Semi Annual Payment, First Payment	Dec. 31, 2013 Senior Notes 5.75% Senior Notes Semi Annual Payment, Second Payment	Oct. 04, 2013 Senior Notes 7.0 % Senior Notes	Dec. 31, 2013 Senior Notes 7.0 % Senior Notes	Dec. 31, 2012 Senior Notes 7.0 % Senior Notes	Dec. 31, 2011 Senior Notes 7.0 % Senior Notes
Debt Instrument [Line Items]
Principal amount of senior notes													$ 265,000,000	$ 265,000,000
Interest rate stated on senior notes	7.00%								7.00%				5.75%	5.75%					7.00%
Senior notes due date									May 01, 2016				Oct. 15, 2023						May 01, 2016
Net proceeds from issuance of senior notes														263,000,000
Unamortized discount												1,700,000
Outstanding principal amount of senior notes												263,300,000
Call premium on redemption of Senior Notes	(17,895,000)								(17,895,000)									17,900,000
Fair value of senior notes															277,600,000					123,200,000
Interest expense on senior notes																				8,200,000	8,200,000
Effective interest rate related to senior notes															5.86%
Interest payment date on senior notes																--04-15	--10-15
Interest expense	$ 4,351,000	$ 2,053,000	$ 2,052,000	$ 2,051,000	$ 2,051,000	$ 2,049,000	$ 2,049,000	$ 2,049,000	$ 10,507,000	$ 8,198,000	$ 8,188,000	$ 10,500,000
Debt instrument, covenant compliance															As of December 31, 2013, the Company was in compliance with all such covenants.