Schedule I - Dividends from Subsidiaries - Schedule of Quarterly Cash Dividends to Common Stockholders (Detail) - $ / shares									1 Months Ended			12 Months Ended
	Sep. 19, 2016	Jun. 08, 2016	Feb. 22, 2016	Jan. 05, 2016	Sep. 16, 2015	Jun. 10, 2015	Mar. 03, 2015	Jan. 05, 2015	Sep. 30, 2014	May 31, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Dividends Payable [Line Items]
Cash dividends declared per share												$ 0.73	$ 0.84	$ 0.62
Q4 2015 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date												Jan. 15, 2016
Cash dividends payable date												Jan. 22, 2016
Cash dividends declared per share				$ 0.21								$ 0.21
Q1 2016 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date												Mar. 14, 2016
Cash dividends payable date												Apr. 01, 2016
Cash dividends declared per share			$ 0.21									$ 0.21
Q2 2016 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date												Jun. 20, 2016
Cash dividends payable date												Jul. 01, 2016
Cash dividends declared per share		$ 0.21										$ 0.21
Q3 2016 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date												Sep. 29, 2016
Cash dividends payable date												Oct. 07, 2016
Cash dividends declared per share	$ 0.10											$ 0.10
Q4 2014 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date													Jan. 13, 2015
Cash dividends payable date													Jan. 22, 2015
Cash dividends declared per share								$ 0.21					$ 0.21
Q1 2015 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date													Mar. 13, 2015
Cash dividends payable date													Apr. 01, 2015
Cash dividends declared per share							$ 0.21						$ 0.21
Q2 2015 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date													Jun. 22, 2015
Cash dividends payable date													Jul. 01, 2015
Cash dividends declared per share						$ 0.21							$ 0.21
Q3 2015 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date													Sep. 29, 2015
Cash dividends payable date													Oct. 06, 2015
Cash dividends declared per share					$ 0.21								$ 0.21
Q1 2014 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date														Mar. 20, 2014
Cash dividends payable date														Apr. 01, 2014
Cash dividends declared per share											$ 0.20			$ 0.20
Q2 2014 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date														Jun. 20, 2014
Cash dividends payable date														Jul. 01, 2014
Cash dividends declared per share										$ 0.21				$ 0.21
Q3 2014 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date														Sep. 29, 2014
Cash dividends payable date														Oct. 06, 2014
Cash dividends declared per share									$ 0.21					$ 0.21
Parent Company [Member] | Q4 2015 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date												Jan. 15, 2016
Cash dividends payable date												Jan. 22, 2016
Cash dividends declared per share												$ 0.21
Parent Company [Member] | Q1 2016 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date												Mar. 14, 2016
Cash dividends payable date												Apr. 01, 2016
Cash dividends declared per share												$ 0.21
Parent Company [Member] | Q2 2016 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date												Jun. 20, 2016
Cash dividends payable date												Jul. 01, 2016
Cash dividends declared per share												$ 0.21
Parent Company [Member] | Q3 2016 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date												Sep. 29, 2016
Cash dividends payable date												Oct. 07, 2016
Cash dividends declared per share												$ 0.10
Parent Company [Member] | Q4 2014 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date													Jan. 13, 2015
Cash dividends payable date													Jan. 22, 2015
Cash dividends declared per share													$ 0.21
Parent Company [Member] | Q1 2015 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date													Mar. 13, 2015
Cash dividends payable date													Apr. 01, 2015
Cash dividends declared per share													$ 0.21
Parent Company [Member] | Q2 2015 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date													Jun. 22, 2015
Cash dividends payable date													Jul. 01, 2015
Cash dividends declared per share													$ 0.21
Parent Company [Member] | Q3 2015 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date													Sep. 29, 2015
Cash dividends payable date													Oct. 06, 2015
Cash dividends declared per share													$ 0.21
Parent Company [Member] | Q1 2014 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date														Mar. 20, 2014
Cash dividends payable date														Apr. 01, 2014
Cash dividends declared per share														$ 0.20
Parent Company [Member] | Q2 2014 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date														Jun. 20, 2014
Cash dividends payable date														Jul. 01, 2014
Cash dividends declared per share														$ 0.21
Parent Company [Member] | Q3 2014 Declaration [Member]
Dividends Payable [Line Items]
Cash dividends record date														Sep. 29, 2014
Cash dividends payable date														Oct. 06, 2014
Cash dividends declared per share														$ 0.21