Schedule I - Condensed Statements of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash Flows From Operating Activities:
Net income	$ 49,919	$ 51,920	$ 74,221
Adjustments to reconcile net income to net cash provided by operating activities:
Net cash provided by operating activities	261,532	286,461	299,440
Cash Flows From Investing Activities:
Net cash used in investing activities	(156,546)	(166,376)	(204,318)
Cash Flows From Financing Activities:
Proceeds from issuance of common stock, net of underwriter commissions		253,800
Purchase of treasury stock	(60,058)	(44,163)
Dividend paid to common stockholders	(72,113)	(36,175)	(502,977)
Offering costs		(4,694)	(3,665)
Payment of tax withholdings on equity-based compensation	(213)	(852)
Net cash used in financing activities	(177,921)	(48,919)	(116,110)
Change in Cash and Cash Equivalents	(72,935)	71,166	(20,988)
Cash and Cash Equivalents-Beginning of period	116,841	45,675	66,663
Cash and Cash Equivalents-End of period	43,906	116,841	45,675
Supplemental Disclosures of Noncash Financing Activities
Treasury stock purchases settled in January 2015	5,650
Parent Company [Member]
Cash Flows From Operating Activities:
Net income	49,919	51,920	74,221
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in net income of subsidiary	(49,919)	(51,920)	(74,221)
Dividend received from subsidiary-return on capital	36,056	18,072	0
Net cash provided by operating activities	36,056	18,072	0
Cash Flows From Investing Activities:
Capital contributed to subsidiary		(249,106)	0
Restricted payment from subsidiary	65,708	44,163	0
Dividend received from subsidiary-return of capital	36,056	18,072	500,000
Net cash used in investing activities	101,764	(186,871)	500,000
Cash Flows From Financing Activities:
Proceeds from issuance of common stock, net of underwriter commissions		253,800	0
Purchase of treasury stock	(60,058)	(44,163)	0
Dividend paid to common stockholders	(72,113)	(36,175)	(502,977)
Offering costs		(4,694)	0
Payment of tax withholdings on equity-based compensation	37		0
Net cash used in financing activities	(132,134)	168,768	(502,977)
Change in Cash and Cash Equivalents	5,686	(31)	(2,977)
Cash and Cash Equivalents-Beginning of period	172	203	3,180
Cash and Cash Equivalents-End of period	5,858	172	203
Supplemental Disclosures of Noncash Financing Activities
Dividends declared, but unpaid	172	17,939	203
Treasury stock purchases settled in January 2015	$ 5,650		$ 0