Long-Term Debt - Additional Information (Detail) (USD $)	3 Months Ended		3 Months Ended		0 Months Ended			0 Months Ended					3 Months Ended			3 Months Ended			3 Months Ended		3 Months Ended	12 Months Ended		3 Months Ended						3 Months Ended			0 Months Ended	3 Months Ended						3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 JPM Term Loan [Member]	Dec. 31, 2013 JPM Term Loan [Member]	Jan. 09, 2012 Sun Trust Term Loan [Member]	Mar. 31, 2014 Sun Trust Term Loan [Member]	Dec. 31, 2013 Sun Trust Term Loan [Member]	Jan. 09, 2012 JPM Bridge Facility [Member]	Jan. 09, 2012 JPMorgan Chase Bank, N.A. [Member]	Jan. 09, 2012 Sun Trust Revolver [Member]	Mar. 31, 2014 Sun Trust Revolver [Member]	Dec. 31, 2013 Sun Trust Revolver [Member]	Mar. 31, 2014 Wells Fargo Revolver [Member]	Dec. 31, 2013 Wells Fargo Revolver [Member]	Jun. 30, 2013 Wells Fargo Revolver [Member] Beecher Acquisition [Member]	Mar. 31, 2014 Bank Of America Loan Term Loan [Member]	Dec. 31, 2013 Bank Of America Loan Term Loan [Member]	Jun. 30, 2013 Bank Of America Loan Term Loan [Member] Beecher Acquisition [Member]	Mar. 31, 2014 Private Placement [Member] Series B [Member]	Dec. 31, 2013 Private Placement [Member] Series B [Member]	Mar. 31, 2014 Private Placement [Member] Series A [Member]	Dec. 31, 2013 Private Placement [Member] Series A [Member]	Mar. 31, 2014 Private Placement [Member] Senior Notes[Member]	Mar. 31, 2014 Line of Credit [Member]	Mar. 31, 2014 Line of Credit [Member] Sun Trust Revolver [Member]	Mar. 31, 2014 Line of Credit [Member] Wells Fargo Revolver [Member]	Mar. 31, 2014 Line of Credit [Member] Bank Of America Loan Term Loan [Member]	Mar. 31, 2014 Master Agreement [Member]	Dec. 31, 2013 Master Agreement [Member]	Mar. 31, 2014 Master Agreement [Member] Series C [Member]	Mar. 31, 2014 Master Agreement [Member] Series D [Member]	Mar. 31, 2014 Master Agreement [Member] Series E [Member]	Oct. 12, 2012 New Master Agreement [Member]	Mar. 31, 2014 New Master Agreement [Member]	Dec. 31, 2013 New Master Agreement [Member]	Apr. 17, 2014 Subsequent Event [Member]	Apr. 17, 2014 Subsequent Event [Member] Credit Agreement [Member]	Apr. 17, 2014 Subsequent Event [Member] Facility [Member]	Jun. 30, 2014 Scenario, Forecast [Member]	Mar. 31, 2014 Minimum [Member] LIBOR [Member]	Mar. 31, 2014 Maximum [Member] LIBOR [Member]
Debt Instrument [Line Items]
Unsecured senior notes outstanding	$ 480,000,000	$ 480,000,000	$ 100,000,000	$ 100,000,000		$ 100,000,000	$ 100,000,000												$ 100,000,000	$ 100,000,000	$ 100,000,000		$ 200,000,000					$ 150,000,000	$ 150,000,000	$ 25,000,000	$ 25,000,000	$ 100,000,000		$ 0	$ 0
Debt instrument, issuance date																			Jul. 15, 2004		Sep. 15, 2004									Dec. 22, 2006	Feb. 01, 2008	Sep. 15, 2011
Debt instrument interest rate stated percentage																			6.08%		5.57%									5.66%	5.37%	4.50%
Debt instrument, maturity date													Dec. 31, 2016			Dec. 31, 2016			Jul. 15, 2014		Sep. 15, 2011				Dec. 31, 2016					Dec. 22, 2016	Jan. 15, 2015	Sep. 15, 2018
Notes redeemed																					100,000,000	100,000,000
Maximum shelf facility capacity																												200,000,000					125,000,000
Length of the issuance period of long-term debt (in years)																												3 years					3 years
Long-term debt maturity, period length, maximum (in years)																												Maturity dates, not to exceed ten years						Maturity dates, not to exceed ten years
Revolving and term loan			100,000,000		100,000,000			50,000,000	50,000,000	50,000,000
Increase in revolving credit facility											50,000,000		50,000,000
Potential increased in line of credit facility						150,000,000					100,000,000		100,000,000																							1,850,000,000		500,000,000
Letter of credit usage fee, minimum																								1.00%		1.00%	1.00%
Letter of credit usage fee, maximum																								1.40%		1.40%	1.40%
LIBOR below base rate																								1.00%		1.00%
Availability fees, minimum																								0.175%		0.175%
Availability fees, maximum																								0.25%		0.25%
Interest rate, minimum																								1.00%		1.00%
Interest rate, maximum																								1.40%		1.40%
Borrowings outstanding											0	0	0	0		30,000,000	30,000,000
Adjusted LIBOR Rate			1.00%
Revolving line of credit															50,000,000
Revolving and term loan																		30,000,000									30,000,000
Revolving credit facility remaining amount													30,000,000
30-day LIBOR Rate																																								0.15%	0.15%
30-day Adjusted LIBOR Rate																																								0.19%	0.19%
Unsecured revolving credit facility																																				800,000,000	1,350,000,000
Unsecured term loans																																				$ 550,000,000
Line of credit facility termination period	Apr. 16, 2019
Line of credit facility interest rate above adjusted libor rate	1.375%																																						1.375%