Schedule II - Condensed Financial Information of the Registrant Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Statements of Income and Comprehensive Income
Revenues	$ 206,958	$ 210,085	$ 202,950	$ 199,829	$ 201,042	$ 201,270	$ 197,602	$ 198,039	$ 819,822	$ 797,953	$ 778,797
Expenses									726,540	826,598	695,479
Net income (loss)	$ 11,953	$ 18,597	$ 21,365	$ 12,670	$ 10,290	$ 11,981	$ (1,053)	$ (35,071)	64,585	(13,853)	59,354
Other net comprehensive income, net of taxes									(621)	(12,251)	11,515
Comprehensive income (loss)									63,964	(26,104)	70,869
Registrant
Condensed Statements of Income and Comprehensive Income
Expenses									1,406	1,230	1,264
Net loss									(1,406)	(1,230)	(1,264)
Earnings from consolidated subsidiaries									65,991	(12,623)	60,618
Net income (loss)									64,585	(13,853)	59,354
Other net comprehensive income, net of taxes									(621)	(12,251)	11,515
Comprehensive income (loss)									$ 63,964	$ (26,104)	$ 70,869