Income Taxes - Summary of Reconciliation of the Income Tax Expense at the Statutory Income Tax Rate and the Effective Tax Rate for Income from Continuing Operations before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Income from continuing operations (before-tax)	$ 141,430	$ 51,138	$ 90,027
Income tax at the US statutory federal rate (35%)	49,501	17,898	31,509
Increase (decrease) resulting from:
Rate differential	5,047	1,145	2,380
State income taxes, net of federal benefit	(601)	(337)	271
Dividends paid deduction	(57,109)	(27,873)	(33,345)
Change in valuation allowance	6,174	8,988	(697)
Other items, net	(1,509)	519	608
Income tax expense	$ 1,503	$ 340	$ 726