Dividends (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended	12 Months Ended
		Aug. 15, 2013	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Dividend Declared [Line Items]
Date of Record			Mar. 07, 2016
Date Paid			Mar. 18, 2016
Amount per Common Share		$ 0.25	$ 0.27
Total Dividends	[1]			$ 116,456	$ 116,155	$ 106,817
First Quarter Dividend
Dividend Declared [Line Items]
Date Declared				Feb. 17, 2015	Feb. 14, 2014	Feb. 12, 2013
Date of Record				Mar. 04, 2015	Mar. 04, 2014	Mar. 04, 2013
Date Paid				Mar. 18, 2015	Mar. 19, 2014	Mar. 15, 2013
Amount per Common Share	[2]			$ 0.25	$ 0.25	$ 0.21
Total Dividends	[1]			$ 29,025	$ 29,015	$ 24,325
Second Quarter Dividend
Dividend Declared [Line Items]
Date Declared				May 18, 2015	May 22, 2014	May 24, 2013
Date of Record				Jun. 05, 2015	Jun. 06, 2014	Jun. 06, 2013
Date Paid				Jun. 19, 2015	Jun. 20, 2014	Jun. 20, 2013
Amount per Common Share	[2]			$ 0.25	$ 0.25	$ 0.21
Total Dividends	[1]			$ 29,075	$ 29,030	$ 24,348
Third Quarter Dividend
Dividend Declared [Line Items]
Date Declared				Aug. 20, 2015	Aug. 13, 2014	Aug. 15, 2013
Date of Record				Aug. 31, 2015	Aug. 28, 2014	Aug. 28, 2013
Date Paid				Sep. 11, 2015	Sep. 12, 2014	Sep. 12, 2013
Amount per Common Share	[2]			$ 0.25	$ 0.25	$ 0.25
Total Dividends	[1]			$ 29,080	$ 29,032	$ 28,992
Fourth Quarter Dividend
Dividend Declared [Line Items]
Date Declared				Nov. 13, 2015	Nov. 12, 2014	Nov. 19, 2013
Date of Record				Dec. 02, 2015	Dec. 02, 2014	Dec. 02, 2013
Date Paid				Dec. 16, 2015	Dec. 11, 2014	Dec. 11, 2013
Amount per Common Share	[2]			$ 0.25	$ 0.25	$ 0.25
Total Dividends	[1]			$ 29,276	$ 29,078	$ 29,152

[1] Of the dividends recorded during 2013, 2014 and 2015, $772, $530 and $593, respectively, were related to outstanding restricted stock units and will not be paid until such units vest. See Note 16.

[2] Beginning with the dividend declared on August 15, 2013, the Company's board of directors raised the quarterly dividend to $0.25 per common share.