Summary of Dividends Declared (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Dividends Payable [Line Items]
Payment of dividends to stockholders	$ 38,833	$ 35,621
February 5, 2014
Dividends Payable [Line Items]
Declaration Date	Feb. 05, 2014
Dividend Per Share	$ 0.15
Record Date	Mar. 10, 2014
Payment of dividends to stockholders	19,602
Payment Date	Mar. 27, 2014
April 30, 2014
Dividends Payable [Line Items]
Declaration Date	Apr. 30, 2014
Dividend Per Share	$ 0.15
Record Date	May 30, 2014
Payment of dividends to stockholders	19,231
Payment Date	Jun. 19, 2014
February 5, 2013
Dividends Payable [Line Items]
Declaration Date		Feb. 05, 2013
Dividend Per Share		$ 0.13
Record Date		Mar. 11, 2013
Payment of dividends to stockholders		17,983
Payment Date		Mar. 28, 2013
April 24, 2013
Dividends Payable [Line Items]
Declaration Date		Apr. 24, 2013
Dividend Per Share		$ 0.13
Record Date		May 30, 2013
Payment of dividends to stockholders		$ 17,638
Payment Date		Jun. 19, 2013