Organization and Significant Accounting Policies - Prior Period Adjustment (Details) - USD ($) $ / shares in Units, shares 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
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Decrease in deferred tax asset	$ (73,068,000)				$ (79,994,000)				$ (73,068,000)	$ (79,994,000)
Decrease in deferred tax benefit									6,926,000	(55,018,000)	$ 4,740,000
Balance Sheet Related Disclosures [Abstract]
Gross deferred income tax asset	73,750,000				130,336,000				73,750,000	130,336,000
Valuation allowance	0				(50,031,000)				0	(50,031,000)
Net deferred income tax asset	73,068,000				79,994,000				73,068,000	79,994,000
Retained earnings	217,275,000				219,127,000				217,275,000	219,127,000
Income Statement [Abstract]
Income tax benefit									8,992,000	(53,948,000)	6,582,000
Net income	$ 3,026,000	$ 4,058,000	$ 3,451,000	$ 3,444,000	68,732,000	$ 4,220,000	$ 3,376,000	$ 3,917,000	13,979,000	80,246,000	$ 20,745,000
Statement of Cash Flows [Abstract]
Deferred income tax (benefit) expense									$ (50,000,000)
Net Operating Loss Carryforward Overstatement
Balance Sheet Related Disclosures [Abstract]
Gross deferred income tax asset					130,025,000					130,025,000
Valuation allowance					(50,031,000)					(50,031,000)
Net deferred income tax asset					79,994,000					79,994,000
Retained earnings					219,127,000					219,127,000
Income Statement [Abstract]
Income tax benefit					53,948,000					53,948,000
Net income					$ 68,732,000					$ 80,246,000
Basic net income per common share (usd per share)					$ 3.28					$ 3.74
Basic weighted average common shares outstanding (shares)										21,471,041	21,644,163
Diluted net income per common share (usd per share)					$ 3.28					$ 3.74	$ 0.96
Diluted weighted average common shares outstanding (shares)										21,471,041	21,644,163
Statement of Cash Flows [Abstract]
Deferred income tax (benefit) expense										$ (55,018,000)
Net Operating Loss Carryforward Overstatement | Previously Reported
Balance Sheet Related Disclosures [Abstract]
Gross deferred income tax asset					$ 129,760,000					129,760,000
Valuation allowance					(45,777,000)					(45,777,000)
Net deferred income tax asset					83,983,000					83,983,000
Retained earnings					223,116,000					223,116,000
Income Statement [Abstract]
Income tax benefit					57,937,000					57,937,000
Net income					$ 72,721,000					$ 84,235,000
Basic net income per common share (usd per share)					$ 3.54					$ 3.99
Basic weighted average common shares outstanding (shares)										21,120,268	21,621,466
Diluted net income per common share (usd per share)					$ 3.53					$ 3.98	$ 0.94
Diluted weighted average common shares outstanding (shares)										21,186,750	22,090,770
Statement of Cash Flows [Abstract]
Deferred income tax (benefit) expense										$ (59,007,000)
Net Operating Loss Carryforward Overstatement | Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Decrease in deferred tax asset					$ (4,300,000)					(4,300,000)
Decrease in deferred tax benefit					4,000,000					4,000,000
Balance Sheet Related Disclosures [Abstract]
Gross deferred income tax asset					265,000					265,000
Valuation allowance					(4,254,000)					(4,254,000)
Net deferred income tax asset					(3,989,000)					(3,989,000)
Retained earnings					(3,989,000)					(3,989,000)
Income Statement [Abstract]
Income tax benefit					(3,989,000)					(3,989,000)
Net income					$ (3,989,000)					$ (3,989,000)
Basic net income per common share (usd per share)					$ (0.26)					$ (0.25)
Basic weighted average common shares outstanding (shares)										350,773	22,697
Diluted net income per common share (usd per share)					$ (0.25)					$ (0.24)	$ 0.02
Diluted weighted average common shares outstanding (shares)										284,291	(446,607)
Statement of Cash Flows [Abstract]
Deferred income tax (benefit) expense										$ 3,989,000