Annual report pursuant to Section 13 and 15(d)

Dividends (Detail)

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Dividends (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dividend Declared [Line Items]      
Amount per Share of Common Stock [1] $ 1.16 $ 1.08 $ 1.00
Total Dividends $ 135,637 $ 126,044 $ 116,456
First Quarter Dividend      
Dividend Declared [Line Items]      
Declaration Date Feb. 23, 2017 Feb. 24, 2016 Feb. 17, 2015
Record Date Mar. 08, 2017 Mar. 07, 2016 Mar. 04, 2015
Payable Date Mar. 20, 2017 Mar. 18, 2016 Mar. 18, 2015
Amount per Share of Common Stock [1] $ 0.29 $ 0.27 $ 0.25
Total Dividends $ 33,912 $ 31,544 $ 29,025
Second Quarter Dividend      
Dividend Declared [Line Items]      
Declaration Date May 25, 2017 May 26, 2016 May 18, 2015
Record Date Jun. 08, 2017 Jun. 08, 2016 Jun. 05, 2015
Payable Date Jun. 22, 2017 Jun. 22, 2016 Jun. 19, 2015
Amount per Share of Common Stock [1] $ 0.29 $ 0.27 $ 0.25
Total Dividends $ 33,904 $ 31,459 $ 29,075
Third Quarter Dividend      
Dividend Declared [Line Items]      
Declaration Date Aug. 10, 2017 Aug. 18, 2016 Aug. 20, 2015
Record Date Aug. 31, 2017 Aug. 31, 2016 Aug. 31, 2015
Payable Date Sep. 13, 2017 Sep. 13, 2016 Sep. 11, 2015
Amount per Share of Common Stock [1] $ 0.29 $ 0.27 $ 0.25
Total Dividends $ 33,911 $ 31,473 $ 29,080
Fourth Quarter Dividend      
Dividend Declared [Line Items]      
Declaration Date Nov. 17, 2017 Nov. 16, 2016 Nov. 13, 2015
Record Date Dec. 01, 2017 Dec. 02, 2016 Dec. 02, 2015
Payable Date Dec. 15, 2017 Dec. 16, 2016 Dec. 16, 2015
Amount per Share of Common Stock [1] $ 0.29 $ 0.27 $ 0.25
Total Dividends $ 33,910 $ 31,568 $ 29,276
[1] Beginning with the dividend declared on February 24, 2016, the Company’s board of directors raised the quarterly dividend to $0.27 per common share. Beginning with the dividend declared on February 23, 2017, the Company’s board of directors raised the quarterly dividend to $0.29 per common share.